Code to parse corpus->json on server

markov.clj contains code to parse the corpus server-side, then translate
it to json. It outputs the json as an array of key/value arrays instead of
a map to make serialization/deserialization simple - you can use #(into {}
%) to easily transform the corpus counts to a map.
Modified markov code to accomodate new json.

The new json is slightly different - map holds strings mapped to counts,
instead of containers of strings. Code changed to match.
Adding a cache to speed it up to textgen.

Atom cache maps sentences to generated text, instead of constantly
regenerating the text.