Added a '.mailmap' file for use with grunt-git-authors.

Added ".mailmap":
 - Cleaned up as much as I could.
 - I made the assumption that "<JZA@JZA-R60>" is @jzaefferer.
 - I was able to everyone to a real name except for @clog.

The resulting "AUTHORS.txt" contains contributors who haven't signed the CLA yet... but so does the current version in master.