Add support for arbitrary background colors

Add support for arbitrary background colors

move attr-string parsing logic to its own function

Fix C-noob mistakes

Add helper comments for later

add color_pair_idx to prepare to add the rest of the color combos

Add remainder of color pairs

Should be backwards-compatible? We'll see what breaks over on linux box

Finish, in principle, adding new color combos.

They are not yet accessible with $ATTR(), and $ATT2() isn't done.

Correcting fgbits in color_pair_idx()

Reverting sleep-deprived 'correction'

Let the new colors be accessible by $ATTR()

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