I don't recall when, but the tags on my test_songs nested-album were changed,
which caused some tests to fail. These changes have been reverted and all
tests pass.
Built tests for a delayed semaphore. The idea is that it is a regular
semaphore with a delay prior to releasing the lock (and decrementing the
'value' count). The intent is to restrict the queries per second in a cleaner
way than the previously used Backoff.py module, which will be deprecated. Two
tests were built, one that restricts a dummy request to five requests per
second (musicbrainz restricts to one query per second), and a second test that
makes a thousand dummy requests at one hundred per second.

Following test development, I built TimedSemaphore in the library module by
subclassing threading._Semaphore (threading.Semaphore is a factory function...
WHY PYTHON?!).

All tests pass.
Forgot to add changes made to the 'gui' module in 'ui' after renaming some of
my modules to lowercase. Here's those changes.