v0.9.0

Just like last time, we quietly performed a release, triggered by the course we teach. This allows us to test it in this course. Bug-fixing, and possibly finishing half-done features, can happen in the v0.9.x branch, and we can do further v0.9.x releases whenever we like (suggestions welcome).

In the meantime, we could prepare a changelog and release notes, and then make the next v0.9.x release a more broadly advertised one.

If you can, please switch your non-playground code dependencies to this release version. If you cannot, remember to switch them to 0.10.0-SNAPSHOT as soon as master compiles again.

Any development which is done on v0.9.x should, of course, also be merged into master. The cleanest way to do this is to develop on a personal branch which is branched off master at some point before today, and, when you're finished, merge that branch into both v0.9.x and master. (Careful: Not the other way round.)

Update: Apparently, there are issues with (I would guess) Bintray's delivery network. Currently, Maven artifacts will sometimes only download on the second attempt, failing some builds. Let's see how this develops.