Add a simple script to validate big message behavior

References #21
Properly pass the block to Consumer#consume into the C layer
Pass a pointer to a Hermann::Result into the message delivery callback

Provided that /something/ is ticking the librdkafka reactor underneath, the
Hermann::Result will be updated with the message delivery status when that's
completed.

What's still missing is producer level error calbacks

Fixes #11
Fixes #15
Fixes #17
Tie Hermann::Result#value to the underlying reactor to bring values up to Ruby

This ensures that we're getting async values out of librdkafka into the calling
Ruby thread. Currently errors aren't being brought up properly, but we're getting there

Example:

    [14:47:30] tyler:Hermann git:(issues/11-producer-feedback*) $ pry -I lib -r 'hermann/producer'
    [1] pry(main)> p = Hermann::Producer.new('topic', 'kafka0.REDACTED.com:6667')
    => #<Hermann::Producer:0x00000803b3b450
    @brokers="kafka0.REDACTED.com:6667",
    @children=[],
    @internal=#<Hermann::Lib::Producer:0x00000803b3b3d8>,
    @topic="topic">
    [2] pry(main)> r = p.push('hello world!')
    => #<Hermann::Result:0x00000803b8cb20
    @producer=
    #<Hermann::Producer:0x00000803b3b450
    @brokers="kafka0.REDACTED.com:6667",
    @children=[#<Hermann::Result:0x00000803b8cb20 ...>],
    @internal=#<Hermann::Lib::Producer:0x00000803b3b3d8>,
    @topic="topic">,
    @reason=nil,
    @state=:unfulfilled,
    @value=nil>
    [3] pry(main)> r.state
    => :unfulfilled
    [4] pry(main)> r.value
    ticking rdkafka reactor
    ticked
    => "hello world!"
    [5] pry(main)> r.state
    => :fulfilled
    [6] pry(main)> r.rejected?
    => false
    [7] pry(main)>
    [14:47:56] tyler:Hermann git:(issues/11-producer-feedback*) $

Fixes #11
Merge pull request #23 from rtyler/issues/11-producer-feedback

Tie Hermann::Result to the librdkafka reactor