There is one key difference between recurring tasks in java.util.concurrent.    ScheduledExecutorService and threadly's interfaces...this fixes the oversight of when a recurring task throws an exception.
This commit solves this in two ways.  The first is to better document threadly's behavior, so it is more obvious how it is different (as I feel threadly's behavior is closer to what most people expect).  The second is to make the wrapper classes that implement ScheduledExecutorService (PriorityScheduledExecutorServiceWrapper / SingleThreadSchedulerServiceWrapper), match the java.util.concurrent behavior (which it already was for scheduleAtFixedRate, just not scheduleWithFixedDelay).  Then the wrapper ScheduledExecutorServiceWrapper's behavior now matches threadly's interface expectations.
I also fixed some small behavior where throwables could be thrown.