[PATCH Cogito] Add -u option to cg-log to show only commits from a specific user

Hi Petr,

the attached patch introduces the -u option for cg-log. Now you can give
a username or a part of an username and only commits with a matching
author or committer will be displayed. Based on a patch from Sean.

Regards

Marcel


Signed-off-by: Marcel Holtmann <marcel@holtmann.org>