[REQ] Allow alternatives to gpg

[Nathan McSween <nwmcsween@xxxxxxxxx>]

I would like to try to make git signing pluggable, this would allow for 
using tools such as signify[1].
Now I'm wondering if this endeavor is worth taking and what would need 
to be changed besides
gpg-interface?

[1] http://man.openbsd.org/signify