[RFC] hit rename

[chshersh]

It's often useful to rename branches (both locally and remotely). I propose to add the hit rename command, which will take care of renaming branches.

For example, if you created a new branch with hit wip (proposed in #159), you can easily rename it under the issue 42 with the following command:

hit rename wip 42

The logic is the following:

1. Rename local branch to the corresponding issue title/random string.
2. Check if the remote branch exists, and rename it as well.