Fix README extension also adding a proper description file.
Fix a typo in rebaseeditor comment
Remove superfluous doc in the main module

Remove superfluous doc in the main module as it is used in the online help and in the man page
Fix "'return' outside function" error
pep8 and whitespace fixups
Ensure GitPython is present for setup

During build, setuptools generates the man page automatically using a
custom class. This in turn uses importing of the project files to allow
argcomplete to construct the command line help. Since import requires
the GitPython project, make sure that setuptools pulls it into the
current workspace for build and install.
Update tests to create isolate git repo

Tests should be run in a pristine git repo where we control how the
commits are created. This allows us to modify the contents of the git
repo to perform more complete set ups to support exercising more
specific senarios in a predicatable fashion.