Support signed git commits

[fredemmott]

https://github.com/blog/2144-gpg-signature-verification

[fredemmott]

@skevy, any chance that this is interesting to you? :p

[skevy]

haha yah! I just started signing my commits the other day :)

[fredemmott]

We'd need this to be optional (most dev boxes wouldn't have access to gpg private keys for testing), but would love a PR ;)