Refinements to git-merge-pull

- Be more prudent about not initiating rebase/merge process if the source and
  target branches don't match the corresponding remote branches.
- Perform the rebase on a separate <branch name>-rebase branch.
- Use colorize to make the output more pretty
- Change the merge commit message slightly.
- Generally be more explicit with git commands around remote and branch. Don't
  assume mapping is setup properly.
Respond to CR
Fix issue with PR summary
Query for PR to merge instead of taking it on CL
Merge pull request #3 from julianwa/feature/git-merge-pull-mods

Looks great, I'll test it out more tomorrow!