Fix docstring of model_locator.ModelData
Use os.path.expanduser() to find homedirectory

This should be more reliable than manually using environment variables.
Add dependencies to numpy and Cython in setup.py

The `install_requires` dependency is important to make sure the target
system fulfills certain requirements independently from whether the
development (and build) system does - even when using binary
distribution.

NOTE: The `setup_requires` dependencies on numpy and Cython are kind of
pointless at the moment, since the modules are imported in the script
beforehand. Still, it seems like good practice to mention those.
Remove distutils as an alternative to setuptools in setup.py

For cpymad setuptools is required anyway since it provides the package
pkg_resources. Allowing distutils only delays the problems.

Setuptools should be available on almost any platform anyways - or at
least easy to install.
Merge pull request #21 from pymad/aesthetic-fixes

Aesthetic fixes

I have no problems with any of this, thanks for cleaning!