Add event queue to TBStateMachine.
Add event queuing.
Update unit tests.

Refers to enhancement #4
Update documentation.

Relates to enhancement #4.
Update documentation.

Relates to enhancement #4.
Update unit test.

Update event processing implementation.
Add unit test for event queueing.

Refers to issue #4
Add unite test for thread safety.

Test event queuing and handling implementation in TBStateMachine.
Add synchronization to -scheduleEvent:data:.
Remove dispatch_sync clause from -handleEvent:data:.
Remove concurrency clause from TBStateMachine documentation since no queue is used anymore.

Refers to issue #5
Fix unit test.

Relates to issue #5
Clean up code.
Merge branch 'feature/event_queue' into develop