Support 8-bit color input

[marlonrichert]

Originally posted by @ckuchimanchi in #18:

znap source trapd00r/LS_COLORS 
znap eval trapd00r/LS_COLORS "$(whence -a dircolors gdircolors) -b LS_COLORS"
znap source marlonrichert/zcolors
znap eval marlonrichert/zcolors "zcolors ${(q)LS_COLORS}"
znap source marlonrichert/zsh-autocomplete

When I run commands after this, all the colors are gone and the auto suggestion in the options have the option list completely blacked out. Demo here - https://asciinema.org/a/DlhcLVJhyEpoZl2xpXm4K7Fn7

Adding support for this requires mapping colors 16 - 255 to colors 0 - 15.