Fix missing comma in reference.

A comma was missing from the output, having been devoured by Pygments.
Specifying it as punctuation.
Fix line width.
Added help for overwriting on install.

If setup.py fails to install the project because the revision number is not
incremented and the same version number has already been installed, it can be
installed with `python setup.py install --force`

On my machine it seems like a regular install will overwrite as well, but the
tip might be helpful for others.