Kadabra

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- Implemented BatchedReceiver
- Publishers now take a list of Metrics to publish instead of a single Metrics
object
- DefaultPublisher only emits output if the number of metrics to publish is
greater than 0
- Channel's complete method takes a list of Metrics objects to mark as complete
- Minor fixes to docs

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- Renamed "Client" to "Kadabra"
- Renamed "Collector" to "MetricsCollector"
- Renamed "get_collector()" to "metrics()"
- Updated docs to reflect these changes

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- Support for Python 2.6, 3.3, 3.4, 3.5, and PyPy
- Changed RedisChannel's message format, no longer uses Base64 encoding, as it
was only increasing message size (not sure why I implemented it in the first
place). This means existing installations of 0.2.0 will need to make sure
their Redis servers are empty (no in-queue or in-progress metrics) before
upgrading. Need to avoid this kind of change in the future, and potentially
version the messages themselves to prevent unhelpful crashes.

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First public release that actually works, packaged properly.

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First public preview release.