Fixed up collisions

Made bouncing off walls a lot nicer, not slowing you down when you
glance off them, and making corners less sticky.
Fixed error with results screen menu

Menu did not wrap correctly in upward (negative) direction.
Changed start button to enter

For consistency with Replay Racer.
Changed timer to frame independent code

Using delta_time for better synchronisation with music.
Final pre-AVCon changes

Updated select screen, reduced win threshold, added back button, readded
drop in/out and fixed possible crash in results screen.
Improved results menu

Removed quit option and made selected option clearer.
Changed boost counting

Changed from number collected to number of directional boosts used.
Added instant boost and separate dodge button
Merged AVCon build into main development line

Restored win threshold, Quit button, controller icons and start prompt
to pre-AVCon, non-DS4 state. Re-enabled character selection. Updated
config for GameMaker v1.3.