Extract div open tags
Extract margin attribute
Some small CSS tweaks
Omit needless semicolons
Omit needless render calls
Omit needless return value
Implicit window reference
Remove getElementById in favour of attributes on window
Rotate with Shift/Ctrl for greater compatibility and shorter code
Merge left and right movement
Tweak left/right key repeat
Use labelled continue to avoid tmp var
Refactor music for reuse by sound effects
Add sound effects (90 bytes over target)
Split with numbers to save quotes
Avoid ceil
Better rotate sound
Fill the readme a bit more
Tweak some for loops
Mention some features I forgot