account for comment delimiters in strings

tests/test_lex.rs

@@ -32,6 +32,12 @@ mod lex_tests {
         assert_eq!(lex(&document).unwrap().to_string(), document);
     }
 
+    #[test]
+    fn test_comment_delim_in_str() {
+        let document = String::from("('#')");
+        assert_eq!(lex(&document).unwrap().to_string(), document);
+    }
+
     #[test]
     fn test_empty_string() {
         let document = String::from("('')");