Use setuptools instead of distutils

distutils `requires` key is virtually useless and does _not_ install required
packages when installing from PyPI. Moreover, the non-pure Pango and Cairo bindings
cannot be installed either which requires manual intervention by the user. Thus
the import check.
Re-name README and make GitHub happy

The README isn't rendered nicely on GitHub if it doesn't provide a file
extension, thus the rename. Uploading on PyPI will is issue a warning that there
is no README but it it can be safely ignored. The preferred way is to use the
long_description key.
Add .gitignore and rules for dist output