Previous Window (base branch changed)

Re-created from #132 to change the base branch and to get the better diffs.

Two notes:
* This pull request contains a change to README.md since this branch was once merged with develop. It should be ok (assuming you'll merge to develop sometime in future.)
* This pull request is based on #142 (fix XIB regressions) assuming all changes in it are ok. If you see problems in #142, I'm more than happy to fix them and then re-merge this pull request if needed. I created this thinking it might be easier for you to merge the two at once in case both look good to you.

Other than that, the patch looks clean (i.e., contains my changes only.)