Add CodeMirror pikchr mode

[Nicholas Bollweg]

Elevator Pitch

Add a CodeMirror mode for pikchr

Prior Art

• https://pikchr.org/home/doc/trunk/doc/grammar.md
  • maybe scrapable?
  • also github mirror could be submoduled, skipping some of the explicit doit tasks:
    • https://github.com/drhsqlite/pikchr
• https://github.com/epmoyer/pikchr_monarch
• https://github.com/MarketSquare/jupyterlab_robotmode

Design Ideas

• make a standalone @deathbeds/codemirror-pikchr package
  • just depend on this in @deathbeds/jupikchr rather than another intermediate package