Merge pull request #31 from rakyll/master

pubsub: Auto-ack messages optionally
pubsub: Implementing subscription listing.
Fixing wrong parameter name on jsdoc.
Merge pull request #32 from rakyll/missing-listings

pubsub: Implementing subscription listing.
Adding regression tests.

* Coverage for datastore.
pubsub: Adding topic listing.
Merge pull request #34 from rakyll/missing-listings

pubsub: Adding topic listing
Simplified test for multiple entities
Merge pull request #33 from silvolu/master

Adding regression tests.
Create Error object for errors returned in the response body.
pubsub: Poll message and emit events.
Add TODO.
Fixed flaky test for Datastore.getAll().

* Order in returned objects is coherent with returned keys, but not necessarily with the keys passed as input.
Adding TODO about the immutability of the subscriptions.
Convert message data to base64 and decode on pull.
Added custom error class for api errors
Merge pull request #36 from silvolu/master

Return Error object for failed Api requests and fixed flaky test.
pubsub: Subscriptions are designed to be persistent. Allow to close without deletion.
pubsub: Subscribe should not involved in persistent subscription creation.
Allow options to be optional.