Add 16-color support

[luca-script]

Checklist

• I've ensured that similar functionality has not already been implemented
• I've ensured that similar functionality has not earlier been proposed and declined
• I've branched off the master branch
• I've merged fresh upstream into my branch recently
• I've ran tox successfully in local environment
• (Not applicable) I've included docstrings and/or documentation and/or examples for my code (if this is a new feature)

Description:

This fixes a very minor issue where bright ANSI escape codes are ignored
It is quite literally 4 lines of code, not sure how it was missed but oh well

[coveralls]

Pull Request Test Coverage Report for Build 11342029412

Details

• 2 of 6 (33.33%) changed or added relevant lines in 1 file are covered.
• 7 unchanged lines in 1 file lost coverage.
• Overall coverage decreased (-0.2%) to 74.594%

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Changes Missing Coverage	Covered Lines	Changed/Added Lines	%
urwid/vterm.py	2	6	33.33%

Files with Coverage Reduction	New Missed Lines	%
urwid/command_map.py	7	74.55%

Totals
Change from base Build 11216432039:	-0.2%
Covered Lines:	9419
Relevant Lines:	12753

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💛 - Coveralls

[penguinolog]

Please add comment explaining colors, because both are 16 colors.
And good to mark that not all terminals will display these colors as bright.