zetta package exposes device registry and peer registry files

[AdamMagaluk]

This helps with allowing to create things like we do in test/fixture/mem_registry.js when running outside the zetta repo.

ex:

var util = require('util');
var levelup = require('levelup');
var memdown = require('memdown');
var DeviceRegistry = require('../../lib/device_registry');

var MemRegistry = module.exports = function() {
  var db = levelup({ db: memdown });
  DeviceRegistry.call(this, { db: db, collection: 'devices' });
}
util.inherits(MemRegistry, DeviceRegistry);

[mdobson]

Signed Off. We'll need to add docs for inheriting from registries.

Registry takes and options object with three potential combos for things.

1. db a levelup instance. Replaces medea. (optional)
2. path a valid path to place a medea database. If db isn't supplied then you need to provide this.
   • defaults to .peers/ for peer registry and .devices/ for the device registry.
3. collection a collection name for calypso. There is a better way to do this, but for now it is needed.