Include .c files in repo.
`pip install git+https://github.com/pydata/pandas.git`

does currently not work because the .pyx files are not being cythonized (not sure why). An easy fix is to include .c files in the git repo which should make it easier for people to deploy.

I used a simple try: import cython in setup.py that cythonizes if cython is installed and uses the .c files otherwise:

https://github.com/hddm-devs/hddm/blob/develop/setup.py#L4
