Make TokenStream's IntoIter derive Clone
Both the wrapper and fallback versions are cloneable.
This brings proc_macro2 in line with proc_macro in terms of this
functionality.
diff --git a/src/lib.rs b/src/lib.rs
index 12faa25..526783a 100644
--- a/src/lib.rs
+++ b/src/lib.rs
@@ -1122,6 +1122,7 @@
///
/// The iteration is "shallow", e.g. the iterator doesn't recurse into
/// delimited groups, and returns whole groups as token trees.
+ #[derive(Clone)]
pub struct IntoIter {
inner: imp::TokenTreeIter,
_marker: marker::PhantomData<Rc<()>>,