299 doc restructure

Here's my first stab at this.

The idea is to trim the main README down to "everything you need to know in 5 minutes", and then break out the rest into topic documents.
We should add here that the API can be explored by hitting the API root. Also, that every resource can be explored by making an `OPTIONS` request to it (maybe a partial copy & paste of the docs that are in the other document).