Add option to de-duplicate contributors by name

to avoid differing email addresses across commits

What do you think about this?

If there are commits by the same name but different email addresses
it will show the address that sorts first... now that I think about it
maybe it would be better to use the one in the most recent commit. :-/

Or do you think it would be better with just explicit include/exclude entries?
I could prepopulate the exclude list with my github email
(since most of my commits don't use my cpan email).