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/ast.rs

@@ -3,10 +3,23 @@ use derivative::Derivative;
 
 #[derive(Debug, Clone, PartialEq, Eq)]
 pub enum Stmt {
-    Assign(Expr, Expr),
+    Assign(AssignStmt),
     Expr(Expr),
 }
 
+#[derive(Debug, Clone, PartialEq, Eq)]
+pub struct AssignStmt {
+    pub lhs: Expr,
+    pub rhs: Expr,
+    pub span: Span,
+}
+
+impl Spanned for AssignStmt {
+    fn span(&self) -> Span {
+        self.span
+    }
+}
+
 #[derive(Debug, Clone, PartialEq, Eq)]
 pub enum Expr {
     Base(BaseExpr),