Add vim Keyword syntax coloring

Orange might not be the best choice, so I'm open to other suggestions,
but I think something is better than nothing.

Close #230.

Signed-off-by: ChaYoung You <yousbe@gmail.com>
Make Git commit summary bold

Uses the gitcommitSummary property from the gitcommit.vim script.
Merge pull request #262 from jcassee/git-summary-emphasis

Make Git commit summary bold
Merge pull request #278 from yous/patch-keyword

Add vim Keyword syntax coloring
Remove duplicated highlightings

See
https://github.com/chriskempson/tomorrow-theme/pull/261#discussion_r20504381.