switch to setuptools

* use entrypoint to generate executable
* find_packages() automatically includes all modules
* requires -> install_requires (remove argparse and subprocess, argparse
  is included in Python 2.7, subprocess had some missing functionality
  before 2.7)
add python-setuptools
add virtualenv-related directories to .gitignore
use pip to directly install from GitHub
themes require configobj 4.7.0 (or higher)