Added complete color theming support for Git

[k4yt3x]

I've noticed that the recently merged Git feature only has one default color, so I completed it. I've added a default color theme for it that looks like this (ignore the conflicted, I didn't bother actually making a repo for it):

... and with this theme of mine:

... it looks like this, works fine:

Edit: also suppressed ErrorKind::NotFound for Git status since if you don't this could happen when you are in a directory that's been deleted:

---

TODO

• Use cargo fmt
• Add necessary tests
• Add changelog entry
• Update default config/theme in README (if applicable)
• Update man page at lsd/doc/lsd.md (if applicable)

[muniu-bot]

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This pull-request has been approved by: k4yt3x

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[codecov-commenter]

Codecov Report

Merging #852 (6ee2cd4) into master (2fe3fcd) will increase coverage by 0.04%.
The diff coverage is 8.57%.

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@@            Coverage Diff             @@
##           master     #852      +/-   ##
==========================================
+ Coverage   86.48%   86.52%   +0.04%     
==========================================
  Files          49       49              
  Lines        4602     4840     +238     
==========================================
+ Hits         3980     4188     +208     
- Misses        622      652      +30     

Impacted Files	Coverage Δ
src/color.rs	43.98% <0.00%> (-5.47%)	⬇️
src/git.rs	90.41% <0.00%> (+2.45%)	⬆️
src/theme/color.rs	76.52% <100.00%> (-2.24%)	⬇️

... and 12 files with indirect coverage changes

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[zwpaper]

thanks @k4yt3x! nice work!