Add new mp3 test test

testing adding new background music
Update README.md
Android back-button actions, pause dialog. Fixes #31, #25.

Pause screen now has a window with two options: resume; quit to title.
The 'quit to title' option has a confirmation window, "quit" or "don't
quit".

Pressing esc (desktop) or back (Android) from the title screen quits the
game; from gameplay pauses; from pause quits to the title screen.
add gold sparks particle system and render on match
add scripts for managing the particle system(s)
implement particle system
Spawn fruits after restarting the game. Fixes #35

Oops.
Enlarged the pause GUI. Fixes #26

Phone screens are very dense, apparently - a low-resolution desktop can
be bigger than a high-resolution phone. Let's just make it all really
big to compensate.

Most web development I've seen uses a whole different layout for mobile
and desktop. Not worth the trouble to do that here, IMO.
remove copyrighted music Issue #33

Using the first music track we have I also have talk to my sound friend
to make more music for future updates
Update README.md
attempt to alter fruit spawning / add bubble effect example for possible later usage
attempt to alter fruit spawning / add bubble effect example for possible later usage
attempt to alter fruit spawning / add bubble effect example for possible later usage
tweak main screen / add new background
tweak main screen / add new background
correct number of fruits is respawned. Fixes #28

Matching sometimes included matched fruits in the list more than once,
so they'd respawn more than once. Matching now returns a HashSet instead
of a list to avoid that. We didn't care about order anyway.

Also affects #54: with fewer fruits, the squish is much less noticeable.
avoid most vertical overlap of fruits. #28

randomize y-coordinate. Also delete some old code and add logging