Add lines to mailmap

Related with #576.
Fix mailmap for Molly Gibsons

Thanks @wking for the tip at
https://github.com/swcarpentry/bc/issues/576#issuecomment-47445298.
Add dbarneche into mailmap
Add dtrap into mailmap
Add Brenna to mailmap
Add AnneTheAgile to mailmap
Merge pull request #577 from r-gaia-cs/mailmap

Add lines to mailmap