Split custom_keyword and custom_punctuation modules
diff --git a/src/custom_punctuation.rs b/src/custom_punctuation.rs
new file mode 100644
index 0000000..9284d02
--- /dev/null
+++ b/src/custom_punctuation.rs
@@ -0,0 +1,301 @@
+// Not public API.
+#[doc(hidden)]
+#[macro_export(local_inner_macros)]
+macro_rules! punct_len {
+    ($mode:ident, +)      => ( 1usize );
+    ($mode:ident, +=)     => ( 2usize );
+    ($mode:ident, &)      => ( 1usize );
+    ($mode:ident, &&)     => ( 2usize );
+    ($mode:ident, &=)     => ( 2usize );
+    ($mode:ident, @)      => ( 1usize );
+    ($mode:ident, !)      => ( 1usize );
+    ($mode:ident, ^)      => ( 1usize );
+    ($mode:ident, ^=)     => ( 2usize );
+    ($mode:ident, :)      => ( 1usize );
+    ($mode:ident, ::)     => ( 2usize );
+    ($mode:ident, ,)      => ( 1usize );
+    ($mode:ident, /)      => ( 1usize );
+    ($mode:ident, /=)     => ( 2usize );
+    ($mode:ident, .)      => ( 1usize );
+    ($mode:ident, ..)     => ( 2usize );
+    ($mode:ident, ...)    => ( 3usize );
+    ($mode:ident, ..=)    => ( 3usize );
+    ($mode:ident, =)      => ( 1usize );
+    ($mode:ident, ==)     => ( 2usize );
+    ($mode:ident, >=)     => ( 2usize );
+    ($mode:ident, >)      => ( 1usize );
+    ($mode:ident, <=)     => ( 2usize );
+    ($mode:ident, <)      => ( 1usize );
+    ($mode:ident, *=)     => ( 2usize );
+    ($mode:ident, !=)     => ( 2usize );
+    ($mode:ident, |)      => ( 1usize );
+    ($mode:ident, |=)     => ( 2usize );
+    ($mode:ident, ||)     => ( 2usize );
+    ($mode:ident, #)      => ( 1usize );
+    ($mode:ident, ?)      => ( 1usize );
+    ($mode:ident, ->)     => ( 2usize );
+    ($mode:ident, <-)     => ( 2usize );
+    ($mode:ident, %)      => ( 1usize );
+    ($mode:ident, %=)     => ( 2usize );
+    ($mode:ident, =>)     => ( 2usize );
+    ($mode:ident, ;)      => ( 1usize );
+    ($mode:ident, <<)     => ( 2usize );
+    ($mode:ident, <<=)    => ( 3usize );
+    ($mode:ident, >>)     => ( 2usize );
+    ($mode:ident, >>=)    => ( 3usize );
+    ($mode:ident, *)      => ( 1usize );
+    ($mode:ident, -)      => ( 1usize );
+    ($mode:ident, -=)     => ( 2usize );
+    ($mode:ident, ~)      => ( 1usize );
+    (lenient, $tt:tt)     => ( 0usize );
+    (strict, $tt:tt)      => ({ unexpected!($tt); 0usize });
+    ($mode:ident, $head:tt $($tail:tt)+) => ( punct_len!($mode, $head) $(+ punct_len!($mode, $tail))+ );
+}
+
+// Not public API.
+#[doc(hidden)]
+#[macro_export]
+macro_rules! unexpected {
+    () => {};
+}
+
+// Not public API.
+#[doc(hidden)]
+#[macro_export]
+macro_rules! stringify_punct {
+    ($($tt:tt)+) => ( concat!($(stringify!($tt)),+) );
+}
+
+// Not public API.
+// Without this, local_inner_macros breaks when looking for concat!
+#[doc(hidden)]
+#[macro_export]
+macro_rules! my_concat {
+    ($($tt:tt)*) => ( concat!($($tt)*) );
+}
+
+/// Define a type that supports parsing and printing a multi-character symbol
+/// as if it were a token.
+///
+/// # Usage
+///
+/// As a convention, it is recommended that this macro be invoked within a
+/// module called `punct` or `punctuation` and that the resulting parser be invoked
+/// with a `punct::` or `punctuation::` prefix.
+///
+/// ```edition2018
+/// mod punct {
+///     syn::custom_punctuation!(LeftRightArrow, <=>);
+/// }
+/// ```
+///
+/// The generated syntax tree node supports the following operations just like
+/// any built-in punctuation token.
+///
+/// - [Peeking] — `input.peek(punct::LeftRightArrow)`
+///
+/// - [Parsing] — `input.parse::<punct::LeftRightArrow>()?`
+///
+/// - [Printing] — `quote!( ... #left_right_arrow ... )`
+///
+/// - Construction from a [`Span`] — `let left_right_arrow = punct::LeftRightArrow(sp)`
+///
+/// - Construction from multiple [`Span`] — `let left_right_arrow = punct::LeftRightArrow([sp, sp, sp])`
+///
+/// - Field access to its spans — `let spans = left_right_arrow.spans`
+///
+/// [Peeking]: parse/struct.ParseBuffer.html#method.peek
+/// [Parsing]: parse/struct.ParseBuffer.html#method.parse
+/// [Printing]: https://docs.rs/quote/0.6/quote/trait.ToTokens.html
+/// [`Span`]: struct.Span.html
+///
+/// # Example
+///
+/// ```edition2018
+/// use syn::{Expr, ExprParen, parenthesized};
+/// use syn::punctuated::Punctuated;
+/// use syn::parse::{Parse, ParseStream, Result};
+/// use syn::token::Paren;
+///
+/// mod punct {
+///     syn::custom_punctuation!(PathSeparator, </>);
+/// }
+///
+/// // (expr) </> (expr) </> (expr) ...
+/// struct PathSegments {
+///     segments: Punctuated<Expr, punct::PathSeparator>,
+/// }
+///
+/// impl Parse for PathSegments {
+///     fn parse(input: ParseStream) -> Result<Self> {
+///         let mut segments = Punctuated::new();
+///
+///         let la = input.lookahead1();
+///         if la.peek(Paren) {
+///             let content;
+///             let paren_token = parenthesized!(content in input);
+///             let expr = Box::new(content.parse()?);
+///             segments.push_value(Expr::Paren(ExprParen { attrs: vec![], paren_token, expr }));
+///         } else {
+///             return Err(la.error());
+///         }
+///
+///         while input.peek(punct::PathSeparator) {
+///             segments.push_punct(input.parse()?);
+///             let content;
+///             let paren_token = parenthesized!(content in input);
+///             let expr = Box::new(content.parse()?);
+///             segments.push_value(Expr::Paren(ExprParen { attrs: vec![], paren_token, expr }));
+///         }
+///
+///         Ok(PathSegments { segments })
+///     }
+/// }
+///
+/// let _: PathSegments = syn::parse_str(r#"("five") </> ("hundred")"#).unwrap();
+/// ```
+///
+#[macro_export(local_inner_macros)]
+macro_rules! custom_punctuation {
+    ($ident:ident, $($tt:tt)+) => {
+        pub struct $ident {
+            pub spans: [$crate::export::Span; punct_len!(lenient, $($tt)+)],
+        }
+
+        #[doc(hidden)]
+        #[allow(non_snake_case)]
+        pub fn $ident<__S: $crate::export::IntoSpans<[$crate::export::Span; punct_len!(lenient, $($tt)+)]>>(
+            spans: __S,
+        ) -> $ident {
+            let _punct_len = punct_len!(strict, $($tt)+);
+            $ident {
+                spans: $crate::export::IntoSpans::into_spans(spans)
+            }
+        }
+
+        impl $crate::export::Default for $ident {
+            fn default() -> Self {
+                $ident($crate::export::Span::call_site())
+            }
+        }
+
+        impl_parse_for_custom_punctuation!($ident, $($tt)+);
+        impl_to_tokens_for_custom_punctuation!($ident, $($tt)+);
+        impl_clone_for_custom_punctuation!($ident, $($tt)+);
+        impl_extra_traits_for_custom_punctuation!($ident, $($tt)+);
+    };
+}
+
+// Not public API.
+#[cfg(feature = "parsing")]
+#[doc(hidden)]
+#[macro_export(local_inner_macros)]
+macro_rules! impl_parse_for_custom_punctuation {
+    ($ident: ident, $($tt:tt)+) => {
+        impl $crate::token::CustomToken for $ident {
+            fn peek(cursor: $crate::buffer::Cursor) -> bool {
+                $crate::token::parsing::peek_punct(cursor, stringify_punct!($($tt)+))
+            }
+
+            fn display() -> &'static $crate::export::str {
+                my_concat!("`", stringify_punct!($($tt)+), "`")
+            }
+        }
+
+        impl $crate::parse::Parse for $ident {
+            fn parse(input: $crate::parse::ParseStream) -> $crate::parse::Result<$ident> {
+                let spans: [$crate::export::Span; punct_len!(lenient, $($tt)+)] =
+                    $crate::token::parsing::punct(input, stringify_punct!($($tt)+))?;
+                Ok($ident(spans))
+            }
+        }
+    };
+}
+
+// Not public API.
+#[cfg(not(feature = "parsing"))]
+#[doc(hidden)]
+#[macro_export]
+macro_rules! impl_parse_for_custom_punctuation {
+    ($ident: ident, $($tt:tt)+) => {};
+}
+
+// Not public API.
+#[cfg(feature = "printing")]
+#[doc(hidden)]
+#[macro_export(local_inner_macros)]
+macro_rules! impl_to_tokens_for_custom_punctuation {
+    ($ident: ident, $($tt:tt)+) => {
+        impl $crate::export::ToTokens for $ident {
+            fn to_tokens(&self, tokens: &mut $crate::export::TokenStream2) {
+                $crate::token::printing::punct(stringify_punct!($($tt)+), &self.spans, tokens)
+            }
+        }
+    };
+}
+
+// Not public API.
+#[cfg(not(feature = "printing"))]
+#[doc(hidden)]
+#[macro_export]
+macro_rules! impl_to_tokens_for_custom_punctuation {
+    ($ident: ident, $($tt:tt)+) => {};
+}
+
+// Not public API.
+#[cfg(feature = "clone-impls")]
+#[doc(hidden)]
+#[macro_export]
+macro_rules! impl_clone_for_custom_punctuation {
+    ($ident: ident, $($tt:tt)+) => {
+        impl $crate::export::Copy for $ident {}
+
+        impl $crate::export::Clone for $ident {
+            fn clone(&self) -> Self {
+                *self
+            }
+        }
+    };
+}
+
+// Not public API.
+#[cfg(not(feature = "clone-impls"))]
+#[doc(hidden)]
+#[macro_export]
+macro_rules! impl_clone_for_custom_punctuation {
+    ($ident: ident, $($tt:tt)+) => {};
+}
+
+// Not public API.
+#[cfg(feature = "extra-traits")]
+#[doc(hidden)]
+#[macro_export(local_inner_macros)]
+macro_rules! impl_extra_traits_for_custom_punctuation {
+    ($ident: ident, $($tt:tt)+) => {
+        impl $crate::export::Debug for $ident {
+            fn fmt(&self, f: &mut $crate::export::Formatter) -> $crate::export::fmt::Result {
+                $crate::export::Formatter::write_str(f, stringify_punct!($($tt)+))
+            }
+        }
+
+        impl $crate::export::Eq for $ident {}
+
+        impl $crate::export::PartialEq for $ident {
+            fn eq(&self, _other: &Self) -> $crate::export::bool {
+                true
+            }
+        }
+
+        impl $crate::export::Hash for $ident {
+            fn hash<__H: $crate::export::Hasher>(&self, _state: &mut __H) {}
+        }
+    };
+}
+
+// Not public API.
+#[cfg(not(feature = "extra-traits"))]
+#[doc(hidden)]
+#[macro_export]
+macro_rules! impl_extra_traits_for_custom_punctuation {
+    ($ident: ident, $($tt:tt)+) => {};
+}