Must be enabled on a per-project basis. You can change this behavior by
setting +magit-hub-enabled-by-default to non-nil (before magit is
loaded).
Magithub has been made opt-in because:
1. Magithub is imposing, asking the user for a token, especially for
users who don't use github (much or at all), but may occasionally
have a project with a github remote.
2. magithub is really slow on first load for medium-to-large repos.
3. It's really easy to enable it through the magithub popup (H C e).
magithub.enabled is saved into the project's .git/config file, so the
setting will persist.
Also added a docstring to +magit-hub-features
Ensures magit buffers are cleaned up after magit-status is closed. Will
defer cleanup on process buffers, until the processes have finished.
Also fixes issue where quitting magit will leave leftover windows.
