Sorting through APIs using visibility

I’ve been helping out on the docs website for `ember-animated` and we’ve ran into a use-case where we would like to enable the users to only see public APIs starting off and give them the opportunity to venture off into private / deprecated APIs later on when they really need to — in order to not overwhelm them starting off.

Here's what I cobbled up as a POC -- as you'll see it's heavily inspired by the Ember docs.


Sam mentioned a re-design of the docs website so I'll hold out on this, but I'd be happy to help it come to life when the time comes.