Changes to documentation, in particular to future and execution context.

version bump to 3.3.1.

fixed bounded-queue full check (#86). added bounded-queue tests.

Stopping actor-cell via `stop' now discards remaining messages.

submit message to for pop queue.

More changes for stop/shutdown and discarding remaining messages.

minor

readme updates.

fixed bug where actor-system shutdown would not close scheduler thread.

fixes to wheel-timer function signature.

allow additional initialization arguments be passed to actor.

additional test for state and init.

version bump