Add/follows

The documentation and tests are incomplete, but the functions for Follows appear to work fine. I will try to fill these out when I have more sleep, but for now I am just waiting on this to merge in order to commit some code in the new notifications web client.
Same that `#unfollow()` method.
We have defined a conventional naming structure for this kind of methods. However nothing prevents us define this naming convention. Maybe @TooTallNate can do his opinion too.

At the moment this name should be `#mine()` and its alias `#state()`.