provisions for recovery, optimizations, cleanup

Added

• Parse speeds on large files reduced by 5-20% by optimizing parse contexts and closures, and unifying the AST_ and CST_ stacks.

• Added the "skip to" expression ( ->), useful for writing recovery rules. The parser will advance over input, one character at time, until the expression matches. Whitespace and comments will be skipped at each step.

• Added the any expression ( /./) for matching the next character in the input.

• The ANTLR_ grammar for Python3_ to the g2e example, and udate g2e to handle more ANTLR_ syntax.

• Check typing with Mypy_.

Changed

• Removed the very old regex example.

• Make parse traces more compact. Add a sample to the docs.

• Explain Grako_ compatibility in docs.