Feature: support co-authors

[jpmcb]

pizza/pkg/server/server.go

Lines 229 to 230 in f2c25cd

	// TODO - if there is a co-author, should handle adding that person on
	// the commit as well.

It'd be great if we could start supporting co-authors and some of the other edge cases that are fairly common in large git projects.

This would take some investigation into the go-git library to see if they support this or not.