Learn to code

Closes #295. This is a total-beginner-focused class, ported from http://codelikethis.com .

I still want to add an "insta-deck" button (see the "Slides" button on http://codelikethis.com/lessons/learn_to_code/learn_to_code to see what I mean) and better page-to-page links but it's probably okay to teach as is.