feat(receive-pack) read-only

[themihai]

This is a feature request to support receive-pack and basically a git server in read-only mode. The implementation could be used to "mirror" an existing repository(and perhaps apply a different ACL) or create and serve in-memory repositories on the fly.

[smola]

We have work in progress for this.

[smola]

The low level work is done (#190), including a clone of the "git-receive-pack" command, see: https://github.com/src-d/go-git/blob/master/cli/go-git/receive_pack.go

Further work will include full git:// and ssh:// servers.