Implement Couchdb / Pouchdb backend

[orolle]

Hi Reid,
saw your recent talk (https://www.youtube.com/watch?v=U4ckAGtv_OI) and it inspired me!

Couchdb is a json document database written in erlang and got ported to javascript (Pouchdb). Couchdb is built on top of an immutable data structure, is able to synchronize databases und allows to listen for live database changes. Its weak spot is its weak query-ability (no joins available) where datalog excells at.

I want to research: First that a couchdb database instance is referable via its unique URL which can be used as a namespace and allow queries across databases. Secondly couchdb provides a sequence id index ("_seq"; transactions in time order) to query data across time.

1. Translate a query plan to a set of Couchdb Mango queries.
2. Execute Mango queries (asynchronously in browser-land) and stream results for lazy processing
3. Use shelvings query processing logic to merge mango results to generate final result