gist versions

[bkatiemills]

I'm a bit concerned about gists for these exercises as the exercises continue to evolve - they need to be versioned so that multiple versions of the course are supported simultaneously.

We can address this by moving all gists into files in a public repo, and replacing the gist link with a link to the raw files. Then we can branch and version in lockstep with the exercises. @xijing-zhang we can start this for ee2.1-v1.0; leave the gists up for older versions.

[bkatiemills]

Actually, the public repo could even be another folder in this repo - then people would just have all of them when they clone the labs.