ANN: nose2 development moved to github

[jason pellerin]

As discussed lately, nose2 development has also moved to github:

https://github.com/nose-devs/nose2

For the time being, no decisions have been made about whether to
continue tracking the (idle?) unittest2 plugins branch or go in a
different direction for nose2. The original goals of making nose2
smaller and less tied to unittest versions shipping with each python
release are still the goals I have in mind -- the question is whether
the unittest2 plugins branch is the way to get there.

JP