Upgraded to 1.2 - final major revision

It's done!  This will be last major update before the I Can't Draw jam ends tomorrow night.  There are a few minor issues that I may try to fix, but I don't have any more significant changes planned.  Here's what's new:

- Added some simple sound effects.

- Added new background graphics to all three stages.

- Eliminated remaining instances of choppy motion.

- Improved sine wave motion.

- Numerous small fixes and gameplay tweaks.

Known issues, which I will probably try to clean up for a 1.2.1 release:

- Defeated enemies may sometimes stick to moving platforms in odd positions.  This is to stop them from bouncing or jittering on those platforms, but the collision check here is very basic.

- Hitting the edge of the diagonally-moving hand in the graveyard can cause some jumpy movement.