Add preliminary support for setting the contrast. (#40)
Add preliminary support for setting the contrast. (#40)

The original Vim theme allowed setting the background colour for one of
three different 'contrast' options: soft, medium, and hard.

This commit allows setting a `gruvbox-contrast` variable to control which
background colour the theme uses, e.g.

(setq gruvbox-contrast 'soft)

for the soft variant.
zzgraph/emacs-theme-gruvbox,ninrod/gruvbox-theme,greduan/emacs-theme-gruvbox,zzgraph/emacs-theme-gruvbox,greduan/emacs-theme-gruvbox,greduan/emacs-theme-gruvbox,zzgraph/emacs-theme-gruvbox,ninrod/gruvbox-theme