Lexer improvements

[badochov]

• fixes #1687 #1688 Additionaly:
• changes newline_re so that it doesn't have group and doesn't require [::2] after split
• simplified Tuple[Failure] to Failure
• used faster isspace instead of regex

Checklist:

• [x] Add or update relevant docs, in the docs folder and in code.
• [x] Add an entry in CHANGES.rst summarizing the change and linking to the issue.
• [x] Add .. versionchanged:: entries in any relevant code docs.
• [x] Run pre-commit hooks and fix any issues.
• [x] Run pytest and tox, no tests failed.