add :trail option for starting the cluster in... well, trailing mode.

 - the current implementation assumes that topics should be read from the
   starts but we have use cases where we only cares about what comes
   next (especially for topics where we keep messages for long periods
   of time)
 - initially wanted to support an :offset option butit became too messy too
   quickly
Merge branch 'master' of https://github.com/davideauee/poseidon_cluster into trailing
Bumped bundle
Updated Readme
Merge pull request #1 from davideauee/trailing

add :trail option for starting the cluster in... well, trailing mode.
Merge pull request #6 from bjhaid/patch-1

Updated Readme
Poseidon(0.0.5 pre1)'s TopicMetadata patitions method became private. use alternative method available_partitions
Poseidon::BrokerPool(~> 0.0.4) doesn't provide default value for socket_timeout_ms
Merge pull request #8 from kssminus/master

Poseidon(0.0.5 pre1)'s TopicMetadata patitions method became private. us...