message: Add lots more lexer escape character tests
  Summary: Test lots of corner cases, especially around error reporting and errors. Discovered one bug in the process.
diff: @@ -207,6 +207,8 @@ impl<'a> Lexer<'a> {
  if count >= min {
  it.unnext(c);
  break;
  + } else {
  + return Err(());
  }
  }
  Some(v) => {
  