merge in mikehelmick/edugit-scripts

:warning: **WIP** :warning: 

In walking a bunch of people through [the GitHub classroom guide](https://education.github.com/guide) the past few days, I've been realizing what a hassle it is, and that we need to make these steps concrete and easily repeatable via code.

@mikehelmick's [edugit-scripts](https://github.com/mikehelmick/edugit-scripts) are awesome, and are efforts that this project shouldn't duplicate.  edugit-scripts would be easier to install as a gem so that dependencies don't need to be installed separately, and I *love* the "teachers_pet" name, so figured I might as well merge in this direction.

This PR folds his code in as executables, though there is still lots more work to be done.  Current usage, structural and coding style inconsistencies aside, just wanted to gauge interest from both of you.  I have lots of ideas for post-merge changes too.

FYI, because [his code is `BSD 3-clause` licensed](https://github.com/mikehelmick/edugit-scripts/blob/master/license.txt), I needed to change the license from MIT to the slightly more strict BSD3, per [this guide](http://www.dwheeler.com/essays/floss-license-slide.html).