Tatsu

* Fix bug in which rule fields were forced on empty ``AST`` (Victorious3)

* Several important refactorings in ``contexts.ParseContext``
* Make ``ignorecase`` settings apply to defined ``keywords``
* Move checking of keywords used as names into ``ParseContext``
* Output of generated parsers again matches that of model parsers
* Improve *"expecting one of:"* messages so elements are in declaration order
* Stop code generation if there are closures over possibly empty expressions
* Preserve name declaration order in returned ``AST``
* Update the bootstrap parser (``tatsu/bootstrap.py``) to the generated parser
* Now generated parser's ``main()`` only outputs the JSON for the parse ``AST``
* Minor version bumped in case the many fixes break backwards-compatibility
* Minor documentation issues fixed
* All tests run with Python 3.8, 3.9, 3.10

* 156 Clarify limitations of left-recursion in PEG (apalala).
* 159 Clean up examples and tutorial, upgrade them to Python 3 (okomarov).
* Test with Python 3.9 (apalala)
* Update CircleCI build (apalala)

- 竜 **TatSu** is now only tested against Python 3.8. Earlier versions of Python are now deprecated, and Python 2.X versions are no longer supported ([apalala](https://github.com/apalala)).
- Apply `nameguard` only if `token[0].isalpha()`. This solves a regression afecting previous TatSu and Grako grammars ([apalala](https://github.com/apalala)).
- Remove `pygraphviz` from develoment requirements, as it doesn't build under Py38 ([apalala](https://github.com/apalala))
- [\56](https://github.com/neogeny/TatSu/issues/56) Include missing `tatsu/g2e/antlr.ebnf` in distribution ([apalala](https://github.com/apalala))
- [\138](https://github.com/neogeny/TatSu/issues/138) Reimplement the calculation of `FIRST`, `FOLLOW`, and `LOOKAHEAD` sets using latest theories. For now, this should improve parser error reporting, but should eventually enable the simplification of parsing of leftrec grammars ([apalala](https://github.com/apalala)).
- [\153](https://github.com/neogeny/TatSu/issues/153) Import ABCs from `collections.abc` ([tirkarthi](https://github.com/tirkarthi))
- Remove support for ``Cython``and ``pypy3`` ([apalala](https://github.com/apalala)).

- The default regexp for whitespace was changed to \`<span class="title-ref">(?s)s+</span>
- Allow empty patterns (`//`) like Python does
- [\65](https://github.com/neogeny/TatSu/issues/65) Allow initial, consecutive, and trailing `namechars`
- [\73](https://github.com/neogeny/TatSu/issues/73) Allow `whitespace :: None` and `whitespace :: False`
- [\75](https://github.com/neogeny/TatSu/issues/75) Complete implemenation of left recursion([Victorious3](https://github.com/Victorious3))
- [\77](https://github.com/neogeny/TatSu/issues/77) Allow `keyword` throughout the grammar
- [\89](https://github.com/neogeny/TatSu/issues/89) Make all attributes defined in the rule present in the resulting `AST` or `Node` even if the associated expression was not parsed
- [\93](https://github.com/neogeny/TatSu/issues/93) Fix trace colorization on Windows
- [\96](https://github.com/neogeny/TatSu/issues/96) Documented each `directive`
- Switched the documentation to the "Alabaster" theme
- Various code and documentation fixes ([davesque](https://github.com/davesque), [nicholasbishop](https://github.com/nicholasbishop), [rayjolt](https://github.com/rayjolt))

* 66 Fix multiline ( (?x) ) patterns not properly supported in grammar (pdw-mb)
* 70 Important upgrade to ModelBuilder and grammar specification of classes for generated nodes. See pull request 78 for details (Victorious3)