Testable ddoc snippets?

[Adam D. Ruppe]

I screwed around on the github website and got to a point where
I think it worked - you should have a pull request for it. The
changes are really trivial, so should be easy to review manually.

I kept the actual editable_code.js on the same domain as the
example code runs because it was easier for me that way. If I change
the server side code, the client side code is right next to it so
that's easy for me to change to match too.