[IMP-dev] IMP 2.1 release

Seems like things are basically ready for the 2.1 release. Tests last night were good and the two open issues on the 2.1 milestone haven't changed recently and seem like we can let them slide (they won't, I think result in significant API or functionality changes). For reference they are: - dock with crosslinking being broken: https://github.com/salilab/imp/issues/560 - compilation warnings in ISD: https://github.com/salilab/imp/issues/539 There will be a 2.1.1 release pretty soon if necessary anyway.

Since there were a couple of commits today, I'll check that nothing breaks in the tests run tonight and if not, create the release branch tomorrow.