extension: add an entity_state_machine, based on the implementation of Ash
state machine: fix runtime error
added function to delete all entities in the world (for example to clean a stage)
changed internal bag of systems to a list of systems, because usually systems are meant to be processed in the same order they have been added and deleting a system should not replace it with the system added last
Merge branch 'dev_fsm' of git://github.com/davidB/dartemis into davidB-dev_fsm
added a test for the EntityStateMachine and made some minor modifications
added contributors
removed the `ComponentProvider.singleton` constructor because it would not work with the current implementation of free lists
updated related documentation
IntervalEntitySystem now provides access to the delta since the last time it has been invoked