👌 IMPROVE: Add CSS support for 8-bit ANSI colours

[thiippal]

This pull request adds support for 8-bit ANSI colours, as discussed in #378.

I got the ANSI to RGB mappings from this repository and converted them into a JSON file.

I then wrote the following script to create the style definitions with hex colour codes:

with open('ansi-to-rgb.json') as file:

	rgb = json.load(file)

	for ansi, rgb in rgb.items():
	
		N = int(ansi)
		HEX = f'#{rgb[0]:02x}{rgb[1]:02x}{rgb[2]:02x}'.upper()
		
		print(f'div.highlight .-Color[class*=-C{N}] \u007b\n  color: {HEX} \n\u007d')
		print(f'div.highlight .-Color[class*=-BGC{N}] \u007b\n  background-color: {HEX} \n\u007d')

Test results:

============================================ test session starts ============================================
platform darwin -- Python 3.9.9, pytest-5.4.3, py-1.11.0, pluggy-0.13.1
rootdir: MyST-NB, inifile: tox.ini
plugins: datadir-1.3.1, regressions-2.2.0, anyio-3.4.0, cov-2.10.1
collected 68 items                                                                                          

tests/test_ansi_lexer.py ...........                                                                  [ 16%]
tests/test_execute.py .....................                                                           [ 47%]
tests/test_glue.py .......                                                                            [ 57%]
tests/test_mystnb_features.py ..                                                                      [ 60%]
tests/test_nb_render.py ............                                                                  [ 77%]
tests/test_parser.py ...                                                                              [ 82%]
tests/test_render_outputs.py .........                                                                [ 95%]
tests/test_text_based.py ...                                                                          [100%]

============================================ 68 passed in 54.55s ============================================

[codecov]

Codecov Report

Merging #379 (52d2b80) into master (9ade331) will not change coverage.
The diff coverage is n/a.

@@           Coverage Diff           @@
##           master     #379   +/-   ##
=======================================
  Coverage   87.35%   87.35%           
=======================================
  Files          12       12           
  Lines        1368     1368           
=======================================
  Hits         1195     1195           
  Misses        173      173           

Flag	Coverage Δ
pytests	87.35% <ø> (ø)

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[chrisjsewell]

Looks great to me ta!