Allow GIT_ env vars for name and email on init
Allow GIT_ env vars for name and email on init

`genesis init` requires git user.name and user.email to be set, but
alternatively, you can now have `GIT_AUTHOR_NAME` and `GIT_AUTHOR_EMAIL`
used.  `GIT_COMMITTER_NAME` and `GIT_COMMITTER_EMAIL` will be set to the
author values if not also present.

starkandwayne/genesis,starkandwayne/genesis,starkandwayne/genesis