Add Git Fetch command

* Supports the following flags: all, append, prune, no-tags, tags
* Added tests for the different flags
Merge pull request #73 from AoDev/feature/git-fetch

Add Git Fetch command
Add upgrade note for gitcommit.
Map commit to what git actually does. Fixes #44.
Add gitadd.
Add --all to add (fixes #38).
Get upstream changes