Improve the documentation comments and generate HTML docs

[lyricsboy]

The doc comments should be updated and expanded for new users.

We can publish a nicely formatted docset as a github pages site associated with this repo.

[zwaldowski]

As mentioned in #22, the use of jazzy handles a lot of the web end of things.

jazzy -m Deferred -g https://github.com/bignerdranch/Deferred -a "Big Nerd Ranch" -u https://github.com/bignerdranch --module-version=2.0.0 -r http://bignerdranch.github.io/Deferred/docs/ --swift-version 2.1

[zwaldowski]

I've published the docs from the tip of #38 to the repo's GitHub Pages endpoint as an example. It's pretty spiffy, and 100% documented!

I'm not sure how we ultimately want to handle this; should the GitHub Pages site be the current docs from master? Or do we keep archival versions? (Realm, for instance, does the latter.)

How we decide to implement it changes the level to which we can automate it. The workflow is currently all manual, but we could potentially get Travis to do it when we merge stuff to master.

[zwaldowski]

Updated to the tip of #29 now that #30 is merged. Check it out!

[zwaldowski]

bignerdranch/CoreDataStack#42 is also relevant!

[zwaldowski]

Completed in #53.