Cache, Templates, online IDE, and more

The main features for this release:

• Grammar caching: It's now possible to cache the results of the LALR grammar analysis, for x2 to x3 faster loading. Use Lark(..., cache=True) or specify a file name. See here: https://lark-parser.readthedocs.io/en/latest/classes/

• Grammar templates: Added support for grammar "functions" that expand in preprocessing. No docs yet, but see here for examples:
  https://github.com/lark-parser/lark/blob/master/tests/test_parser.py#L845

• Lark online IDE: Technically not a feature, but it's possible to run Lark in the browser. Now we also have a simple IDE on github pages: https://lark-parser.github.io/lark/ide/app.html

• Other changes:

  • Improved performance for large grammars

  • More debug prints when in debug mode

  • Better support for PyInstaller

  • Lots of bugfixes: mypy stubs, v_args, docs, and more.