Add GitGutter plugin colors to themes
Merge pull request #22 from mreinhardt/git_gutter_colors

Add GitGutter plugin colors to themes.

Thanks to Michael Reinhardt (@mreinhardt).
Style markup headings the same as constants.
Style tag names and attributes differently.
Remove unused keys/values.
Merge branch 'variant'
Remove empty style/setting blocks
Add selection border and inactive selection colors.
Highlight variable.parameter (same as lang/other variables)
Change the color of markup tags.

Courtesy of FichteFoll. Blame him.
Update diff colors.

Courtesy of FichteFoll. Blame him.

- Give add/delete foreground colors.
- Add a generic markup.changed
Lighten the background of embedded sourcecode.

Courtesy of FichteFoll. Blame him.
[personal] minor adjustment to the theme to suit my desires