Move playerLeft/playerRight into the scene.

Also, remove the unnecessary drawAbsolute calls. They are only needed
when the camera moves, and pong has a fixed camera.
Remove invert function.
Convert global speed var to local.
Move global waitingToStart into scene.
Simplify drawing of dashed center line.
Simplify ball spawning.
Extract movePlayer().
Convert ball global to scene var.
Group paddle handling and ball handling.
Rename playerLeft/Right->left/rightPaddle.
Convert global score vars into scene vars.
Rename scoreLeft/Right-> left/rightScore.
Merge pull request #3 from ericlathrop/remove-globals

Remove globals