Support Beacons.

[fabianfett]

Currently there is no support for iBeacons. Though Apple supports iBeacons with passbook.
Adding beacons should work as the rest of the api.

pass.beacons([{
      "proximityUUID": req.business.beacon,
      "relevantText": "You are here!"
  }]);

In a small test I made it is sufficient to add "beacons" to the TOP_LEVEL var in lib/pass.js.