NF: write __config__.py with compile variables

Write the discovered compile-time variables into a file
``dipy/__config__.py`` so dipy code can act depending on the result of
the compile - for example compile-time presence of openmp.
Merge branch 'config-py-idea' of https://github.com/matthew-brett/dipy into fix_profiles

Conflicts:
	setup.py
Using simpler __setup__.py, suggested by Matthew