change 01 after first testplay

Changes after first feedback from tester Marcusd0  :3

Mapped the S key to down (oopsie oversight)
Improved acceleration in air to allow for (better) steering in air
Improved wallgrabbing/wallsliding muchly by (again) halving the gravity while on wall
tweaked walljump (horizontal acceleration)
Improved dash effect to be more visible
Changed the way dash direction is primarily determined to counter a potential bug
Now allows only one dash in air (same as doublejump/airjump)
Slightly increased dash cooldown time
tweaked (slightly increased) dash speed

Todo:
change the way K looks in the font file to make it less like an H

Maybe:
change slide down slope "animation"?
should walljump refresh airjump?
make an indication of whether you can or cannot dash (/is dash on cooldown)