Adds support for git branch divergence syntax

Hi,

I've added a diverged_status check for those cases when ```git status``` returns something like this:

```bash
On branch dev
Your branch and 'origin/dev' have diverged,
and have 3 and 2 different commits each, respectively.
  (use "git pull" to merge the remote branch into yours)
Changes not staged for commit:
  (use "git add <file>..." to update what will be committed)
  (use "git checkout -- <file>..." to discard changes in working directory)
```

This will render a propmt with this branch info: dev 3⇡ 2⇣