Try to improve performance by using LevelDB

[terrencewwong]

Todo: create a file level-queue.js that implements the AsyncQueue<T> Interface and is backed with LevelDB instead of PouchDB. Then try using this queue in learning-strategy.js instead of pouch-queue. My hypothesis is that this will improve performance.

Explanation: The main data structure used to persist data lives in a file pouch-queue.js

I think performance is suffering by using PouchDB since PouchDB is more than just a simple key-value store. PouchDB keeps track of a revision history for any items you store, this functionality is not required, so we can probably use something more light weight.

Behind the scenes, PouchDB is implemented with LevelDB anyways. The node adapter for LevelDB is a project called levelup more info can be found here: https://github.com/Level/levelup