new: added a ``mako`` output engine with standard ReSTructured text format for reference.
new: pkg: will launch ``./autogen.sh`` automatically. Even if called thanks to ``pip install git+https://github.com/vaab/gitchangelog``.

A hack on 'pure lib' had to be added because data files weren't installed
correctly in case of a distant installation with::

    pip install -v git+https://github.com/vaab/gitchangelog.git@mustache

Resulting with templates not accessible.

Removed setuptools dependency that seemed obsolete and was having bad
side effects.
chg: removed ``pkg`` and ``dev`` commits from default sample changelog output.
fix: very minor spacing adjustement @minor