Add completion hook to end of era

You can now add a completion hook to the end of an era and also the end of an epoch. That means you can get a callback to run when one of these events happens.

Add support for interruptible periods

Epochs can now be marked as being "interruptible". That means that should an action occur in the period between the previous epoch and this interruptible epoch then the action is fired and the epoch gracefully shut down.

Add support for collecting epochs

In this release you're able to define multiple epochs and any actions that occur during the period between epochs will be fired once the next epoch is reached.