Unbundle Six and Cythonize setup by bulding an optional "addons" package

This pull request unbundles Six (available from pypi) and adds some extra options to setup.py, so there will be an additional "addons"-package if Cython is installed on the user's system.  This "addons"-package avoids the need for building the so-extension during runtime (although this probability is still available after the changes) .

For a good reason I've removed the hashbang from libraries' files and also fixed the executable permissions on the files.  A lib should NOT have executable files NOR hashbangs, because the python-files are not intended to be called in "script-like-style", but from inside some python-code (which might be a script).