Support for specifying the branch for the repo

[WALL-EEEEEEE]

First of all, I wanna say thank you for this useful project. And I wander if there are any possibilities to allow user to specify the branch version for the repo. I have a repository with all exercises code of a book. Each exercise is subranched into specific branch. So if I wanna reference a particular exercise, I need to specify the exact branch version. I don't know how to get to do it right now.

Please let me know if it is accessible. And I'm glad to give a pull request if it can be.