Ready for prime time?

This Gem, intended as a companion to @krisleech's wisper, is, as described in the README, principally intended as a testing tool.

The 0.2.0 release introduces a distinction between the new WisperSubscription#payloads_for method, which returns an Array of all payloads received for a specified message, and WisperSubscription#payload_for, which previously functioned as the other method does now, but now returns a single payload (Array of parameters) for the indexth payload of the given message.