(TK-117) Add external API docs

Add some external API docs in the doc folder which detail how
to make requests using the Java and clojure clients.
Oh, I didn't realize they were our classes.  It just seems odd to be writing what appears to be a Javadoc in English: "the first constructor takes one argument, FooConfig, which is a ...."

I would consider writing real Javadocs on those classes and then linking them here, but not a big deal.