Add language definition for Uxntal.

[non]

Add language definition for Uxntal.

Description

Uxntal is an assembly language for the Varvara virtual machine.

Uxntal assmebly is compiled into ROMs. Emulators to run these ROMs exist for a wide variety of hardware.

I found around 268 Uxn repositories on Github and around 1k paths. Given that most projects consist of 1-3 .tal files I believe this meets the criteria for inclusion. Uxn has also been written about in the press.

The samples are MIT-licensed programs taken from the main project:

• mandelbrot.tal
• piano.tal

Checklist:

• [X] I am adding a new extension to a language.
  • [X] The new extension is used in hundreds of repositories on GitHub.com
    • Searching for "uxn" I find 268 repos
    • Searching for "varvara" I find 208 repos
    • Searching for "*.tal" files I find 1k files
  • [X] I have included a real-world usage sample for all extensions added in this PR:
    • Sample source(s):
      • mandelbrot.tal
      • ~piano.tal~ dvd.tal
    • Sample license(s): - MIT - MIT
  • [X] I have included a syntax highlighting grammar: https://github.com/bellinitte/uxntal-vscode
  • [X] I have added a color
    • Hex value: #72dec2
    • Rationale: This green seems to match that used on Uxn pages, e.g. https://wiki.xxiivv.com/site/varvara.html

[non]

Alright, I replaced piano.tal with the much smaller dvd.tal and ran script/update-ids.

[non]

I think this is ready to go, but please let me know if there's anything else missing.