* Uses finite state machine for three states: Closed, Open, Half-Open
* Closed state allows calls through, and on sequential failures exceeding the max# set - transitions to Open state. Intervening successes cause the failure count to reset to 0
* Open state throws a CircuitOpenException on every call until the reset timeout is reached which causes a transition to Half-Open state
* Half-Open state will allow the next single call through, if it succeeds - transition to Closed state, if it fails - transition back to Open state, starting the reset timer again
* Allow configuration for the call and reset timeouts, as well as the maximum number of sequential failures before opening
* Supports async or synchronous call protection
* Callbacks are supported for state entry into Closed, Open, Half-Open. These are run in the supplied execution context
* Both thrown exceptions and calls exceeding max call time are considered failures
* Uses akka scheduler for timer events
* Integrated into File-Based durable mailbox
* Sample documented for other durable mailboxes
* Improved DurableMailboxSpec for stand alone usage
* Changed build to publish DurableMailboxSpec in akka-mailboxes-common-test
* Changed documentation of durable mailboxes and added full example of
how to implement a durable mailbox, with test
* Changed signatures and constructor of MessageDispatcherConfigurator
* Changed Dispatchers.lookup, keep configurators instead of dispatchers
* Removed most of the Dispatchers.newX methods, newDispatcher is still there because of priority mailbox
* How should we make it easy to configure priority mailbox?
* Changed tons tests
* Documentation and ScalaDoc is not updated yet
* Some tests in ActorModelSpec are temporary ignored due to failure
