Clean up the Makefile
Clean up and improve infrastructure scripts

 * The requirements.txt file was narrowed down to just one dependency:
   the python-yaml;
 * The requirements-dev.txt file was renamed to development.txt;
 * The Makefile was rewritten with way less lines of code +make -bash;
 * The setup.py file now reads the version info statically from the
   milieu/version.py file instead of hard-coding it;