Add more expressions to parser, add EOL and newline tokens

* Lexer recognizes semicolons as EOL tokens, and newline tokens
* Parser can be configured to ignore newlines (which is also used
  internally)
* Newlines are allowed in lists, tuples, and parenthesized expressions
* Add a bunch of tests for the new stuff

Signed-off-by: Alek Ratzloff <alekratz@gmail.com>

src/syn/span.rs

@@ -120,6 +120,7 @@ impl Spanned for Span {
     }
 }
 
+/*
 pub struct Sourced<'t, T: Spanned> {
     text: &'t str,
     inner: T,
@@ -136,6 +137,7 @@ impl<T: Spanned> Spanned for Sourced<'_, T> {
         self.inner.span()
     }
 }
+*/
 
 #[cfg(test)]
 mod test {