Added ability to place rests in the files.

I honestly made this in school while bored using the GitHub web editor. If this isn't accepted by the time I have the chance to properly test it, then I'll just accept it myself later. You can accept it if you happen to test it.

The commits combined now allow you to have rests in songs by putting in blank lines. A rest is simply a note that isn't played. That means that rests are still played at the same tempo as the song.

Ex: If tempo = 250ms then two rests pause for 500ms.