[IMP-dev] Preparation for 2.3 release

So, it's about time for the next IMP release. Unless there are good reasons not to, I'll go ahead and do that in a week or two.

If you made any big changes since the 2.2 release, please make sure there's a description of what you changed in the changelog: http://integrativemodeling.org/nightly/doc/html/changelog.html

PMI people: there are still a bunch of broken tests and examples in PMI. It would be great if at least some of those could get fixed before the release. ;) Not a blocker for release though, as I think PMI would still be considered "experimental" at this point. If you need time for any cleanups or bigger changes, please let me know ASAP.

Ben