Refactored structure

- Package name is now bzikarsky/react-gearman
- Namespace is now Zikarsky\React\Gearman
- Moved Gearman\Protocol into Zikarsky\React\Gearman\Command
  Reasoning: All the elements are only about Command creation
  and serialization

Structure is now:

\        : All classes a users directly uses
Command\ : Command creation and serialization
Event\   : All events
Protocol\: Abstraction of certain protocol elements