pyrex: new package

Pyrex is a language that allows you to mix python and C code in a
single .pyx description file.  This file is then rendered into C
code by the pyrexc host tool.  That C file then can be used within
an application build or as part of the normal distutils build
process used to build a Python extension module.

Signed-off-by: Matt Weber <mlweber1@rockwellcollins.com>
Signed-off-by: Peter Korsgaard <peter@korsgaard.com>