Moved verbose mode code to its own method

All verbose mode code moved into its own method and only executed if
verbose mode flag set
Encapsulated listen() checks in listenerChecks()

Didn’t like that I had to use “that” all over my listen() method
because the caller scope changed to an anonymous function (and
therefore “window”) when jumping into the setInterval() call.

Also, I think the work that the listener does could change over time,
while the basic step of listening every x milliseconds won’t. As such,
I think it makes more sense to break the procedures out into a separate
method in case one day it makes sense to add more methods to be
executed during the listen() event.

Also, because of the number of times this._eventListeners[i] was
written into the procedures, I decided to stuff it into a local var at
the top of the for-loop to help avoid typos and in case the listener
structure changes at some point in the future.
Fixes and Tests

EventLoop.addListener(…) now returns the EventListener object that is
created (as it should have all along, of course).

Compressed. cleaned up some code and commits.

Changed testing code to add a new item after all other items have
triggered.