Support for submodule update

[PhilHannent]

I don't see in the source anywhere that you are handling git sub-modules. On some of my repos I need to pull and then run:

git submodule update --init --recursive

It would be great if you could do this as well.

[imsky]

good suggestion, will look into it

[Anahkiasen]

I thought this was about using git-fresh on the submodules themselves which throws an error at the moment but I'd love support for that as well