Improvements to the formatting and language within the javadocs.
Changed the behavior around setting different values within the PriorityScheduledExecutor.  If the value is changed in a way that old workers may exist that need to be cleaned up, we now cleanup on that actual call (instead of waiting for another task to complete first).  In addition I made some small changes inspired from the reduced_string_duplication branch.
Javadoc changes.
Simplified time unit conversion (and fixed a couple places that were technically incorrect, but I don't think were possible to hit)
Did not mean to remove this javadoc
Did an initial implementation of scheduleAtFixedRate.  This does not currently have any unit testing (and thus is not ready to be merged into the main development branches)
Catch this exception from recurring tasks if we are shutting down.
Merge branch 'unstable_staging' into PriorityScheduledExecutorServiceWrapper-scheduleAtFixedRate
Starting to increase functionality in the TestRunnable to track usage in parallel (which currently can only be done from the TestRunnable, although that too is being improved).
More improvements to the TestRunnable for handling when the run is finished, as well as detecting if it ran concurrently.
Implemented unit tests for this new functionality.  I also emphisized that using this functionality should be with caution (but better than just throwing an UnsupportedOperationException)
Reduced some code duplication now that TestRunnable is capable of accepting a delay on construction.
Further code duplication in unit tests reductions.  In addition solved a unit test failure due to always using the native sleep in TestRunnable (which I want to keep since it should represent computational work).  So needed to bring back the SleepThread inner class to TestablePrioritySchedulerTest.
Merge branch 'master' of github.com:threadly/threadly