[Cython] Bugfix release 0.20.1 release candidate

[Robert Bradshaw]

Tarball up at http://cython.org/release/Cython-0.20.1rc1.tar.gz

This is a bugfix only release, primarily to address the sequence
literal multiplication bug, but the set of improvements since the last
release looked relatively safe so I've pulled in everything from
master (if that turns out to be a problem we'll release with just this
big fix).

Let us know if it breaks anything; I hope to get this out soon.

- Robert