Move get_submodule_paths() to a standalone method
Add option to specify configuration file in git_config()
Add option to replace submodules URL using login name

If update_gitmodules is True, the submodules URL registered in the .gitmodules are modified using the login name of the Github connection.
Recursively pass the new update_gitmodules option
Expose update-gitmodules at the command level (merger & update-submodules)
Merge pull request #72 from sbesson/gitmodules

Gitmodules update