Added remaining in progress keywords

As promised in #25 and #28, we are adding in the reamining `in-progress` keywords. Sorry for the large PR but flat file test cases are quite bulky with git repos =(

In this PR:

- Add test case for interrupted `git am`, `git rebase`, `git rebase --interactive`, `git rebase --merge`, `git cherry-pick`
- Add test case for incomplete `git bisect`, `git revert`
- Added matching functionality for test cases in `.bash_prompt`
- Added demo script to generate screenshot for showcase but decided against placing in README

![Example keywords](https://raw.github.com/twolfson/sexy-bash-prompt/e10f9e2cda7032dd7ba0b4c66cdf969bf3a0be20/docs/in-progress.png)