Switch from using Buster to using qUnit
Stop using JSONP calls for GET requests

JONP requests weren't needed and they interfiered with Sinon's spy()
methods.
Fix the API command for getting gist comments

The API command that gets generated when requesting data about a single
comment is wrong. I've fixed it to match what's in the API docs.
Reformat generateAuthorizationLink test
Switch from Buster to Qunit
Add test file reference for getGistComments
Create unit tests for authenticateUser method