Switch over to pbr

[ariddell]

Switch to pbr if possible (Cython support?) to make releases simpler.

[ariddell]

This isn't trivial but it seems possible. The strategy looks like to use a hook to generate the appropriate .c files using cython and then build using pbr as if the cython extensions were normal C extensions. Not sure about all the special includes needed for GRNG.

[ariddell]

If Cython support is required, this is trivial. The custom sdist command might cause some problems.