This reverts commit 81b7760c.

Closes #4590

Closes #4585

Issue #4497

Closes #4499

Closes #4573

Closes #4568

To forbid using the comment strings from their inner modes

Closes #4562

Closes #4563

Closes #4472

Closes #4553

  - Update keywords (remove `ifdef`. add `select`, `uninitialized` and `__END_LINE__`.)
  - Add new string literals (%q string and here docs).
  - Remove global variable syntax (because it is no longer supported.)
  - Improve indentation (fix #3887, and correct indentation of `abstract class`)

Closes #4545

Issue #4528

Closes #4528

Closes #4519

Reference: https://golang.org/pkg/builtin/#rune

Closes #4506

Closes #4505

Issue #4494

Closes #4484

Issue #4476

Closes #4468

Closes #4473