Unconditionally provide Error and Result types

These are not noticeable in compile time so don't need to be behind a
feature.
diff --git a/src/error.rs b/src/error.rs
index 0e482e6..53069da 100644
--- a/src/error.rs
+++ b/src/error.rs
@@ -16,6 +16,7 @@
 #[cfg(feature = "printing")]
 use quote::ToTokens;
 
+#[cfg(feature = "parsing")]
 use buffer::Cursor;
 use thread::ThreadBound;
 
@@ -172,6 +173,7 @@
     }
 }
 
+#[cfg(feature = "parsing")]
 pub fn new_at<T: Display>(scope: Span, cursor: Cursor, message: T) -> Error {
     if cursor.eof() {
         Error::new(scope, format!("unexpected end of input, {}", message))