Add lexer, parser, ast, and basic command line interaction

* Add lexer and parser using lrpar crate
* AST is added and constructed via lexer and parser
* Command line program `not` will read a file and parse it

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

src/syn/parser.y

@@ -12,6 +12,7 @@ Body -> Result<Vec<Stmt>>:
         Body 'EOL' Stmt {
             flatten($1, $3)
         }
+    |   Body 'EOL' { $1 }
     |   Stmt { Ok(vec![$1?]) }
     |   { Ok(Vec::new()) }
     ;
@@ -48,6 +49,9 @@ AccessExpr -> Result<Expr>:
         AtomExpr AccessExprTail {
             Ok(AccessExpr::new_expr($1?, $2?))
         }
+    |   AtomExpr {
+            Ok(AccessExpr::new_expr($1?, Default::default()))
+        }
     ;
 
 AccessExprTail -> Result<Vec<Access>>: