[WIP] Import cluster implementation by @bsm

[wvanbergen]

This is a WIP to bring @bsm's cluster implementation to Sarama.

TODO / discussion:

• Do we want to keep it in a separate package or merge it into the main sarama package?
• Tests need to be rewritten to fit the rest of the library.
• Let's use a standard UUID instead of the custom guid implementation.

/cc @eapache @burke

[wvanbergen]

This is not working for me; it is always empty because I think this is a synchronous channel in the latest Sarama release. When I remove the check, and just wait on <-events instead, it works. However, the batching doesn't really make sense anymore with that change.

[ORBAT]

As a side note, on the current master (f503eb0) the consumer event channel can be buffered (and the default buffer size is 16.) The way I understand it, the len(events) check should only fail if the channel isn't buffered; unbuffered channels always have a length of 0: http://play.golang.org/p/mZ7aWiY0ax

[wvanbergen]

I moved this effort to https://github.com/wvanbergen/kafka