Playsound

* Adds in an automated test suite.
* Non-ascii filepaths and filepaths with spaces should now consistently work.
* Path objects are supported now.

* Fixes bug that prevented relative paths from working on OS X.

* Now uses NSSound.initWithContentsOfURL_byReference_ on OS X
instead of NSSound.initWithContentsOfFile_byReference_. This allows it to
handle both local file paths and URLs. This capability was already
unintentionally present on Windows by using windll.winmm. Since I lack a
Linux machine to test on, and nobody is offering assistance, many things
that work well on OS X and Windows probably don't work at all on Linux.

* Changed from using winsound.PlaySound on Windows to windll.winmm.
Appears to be just as common as winsound, and has the advantage of playing
more file formats, such as MP3, than winsound (which only plays WAVE as
far as I can tell).

* Initial commit