[Cython] Cython 0.15 release

[Robert Bradshaw]

We're long overdue for a release, and this week would be a good one
for me to push one out. Hudson
https://sage.math.washington.edu:8091/hudson is looking in pretty good
shape, and though I know we've got a big pile of stuff currently in
progress, we've also got a big backlog of stuff to get out. I'd like
to finish looking at https://github.com/cython/cython/pull/38 , are
there any other changes that people want to urgently get in? Also,
I've started http://wiki.cython.org/ReleaseNotes-0.15 , feel free to
edit if you think anything should be highlighted.

- Robert