Subject: Cython 0.28.4

From: Leo Famulari <[email-masked]>
Date: Thu, 19 Jul 2018 17:06:19 -0400

I tested this with Borg, after making sure the generated C files in
Borg's source code had been deleted.

Should we do this on master? It takes quite a while to build Cython, so
it might be nice to do it on its own branch, or on the staging branch.