Simplify code by using the kart's normal.
Try better computation of heading (which might be better if the kart
is not in the xz plane).
Avoid use of quaternions, simplify rescue animation. Heading is currently
unchanged, but it looks ok-ish.
Simplify up-offset computation.
Fixed rescue transform: the heading rotation need to be done around
(0,1,0), not around the normal, and the order of rotation needs to be
first the heading rotation, then pitch/roll to make the kart parallel
to the ground.
Merge branch 'walldriving' of github.com:lurk26/stk-code into walldriving