Pre-test. Working cluster, but no fault tolerance

Save current state. Alter documentation, write some basic tests,
add an example of looped ping, make cluster working (until any error :-)
TODO:
  * Write watchdog to reconnect fallen nodes
  * Dig into situation where missed cluster node returns and gets
    flushed.
  * Maybe should overload AnyEvent::DBD::mysql connect method to
    signal it's state to cluster by calling some hook.
  * Maybe write tests for building dsn string from hash