Create a websocket driver

[tonyhb]

In order to get live feeds for data we should create a websocket component.

Questions:

• [ ] How do we differentiate feeds within queries and source definitions?

If the websocket endpoint returns a live feed for use with subscriptions (#35) we should indicate that the source definition returns a feed:

manager.fromSocket([
  {
    meta: {
      url: '/api/v0/eents',
      // tbd... 
  },
  returns: Event.feed(), // TBD: is this a feed for a single item or a list of items?
])