Added list of contributors

I know git(hub) gives us much of this, but it doesn't credit the
"copilot" from pairing, so this is a way to list *everyone* who's
contributed to our code, even if they didn't do the actual commit with
their own github account.
Broke out "committers" and "contributors"

I figured this would make it easier to show who's a good person to ask
for help or information, while still crediting everyone who's
contributed.
Merge pull request #206 from Skud/contributors

Added list of contributors