Add colorizer and importer for 竜 TatSu files

[tbpassin]

竜 TatSu is a PEG parser generator that uses a version of EBNF for its rules.
See https://tatsu.readthedocs.io/en/stable/intro.html

[edreamleo]

@tbpassin I'll delegate this one to you :-) Please feel free to ask for help.

[tbpassin]

Pretty sure I'll be asking! - since I don't know much about the colorizer, the importers or 竜 TatSu. So don't be looking for a PR in a hurry.

[edreamleo]

@tbpassin The tasks:

• Support @language tatsu. See app.__init__ (helpers contain language dicts).
• Create leo/modes/tatsu.py.
  All files in leo/modes/ call pattern matchers in class JEditColorizer(BaseColorizer)inleoColorizer.py. Organize tatsu.pyalong the lines ofleo/modes/python.py`.

Running Leo with --trace=coloring shows superb traces in the console.