For the time being we don't support writing a description for those, preferring
having all details in the method's description.
Using self-closing tags saves half the lines, and prevents contributors from
thinking that they should write the argument or return documentation there.
Fixing by applying the movement in two steps, first the platform
movement, and then the body movement. Plus, add the platform movement
when we are on_wall.
MODE_DYNAMIC instead of MODE_RIGID
MODE_DYNAMIC_LOCKED instead of MODE_CHARACTER
No more special case for sleeping behavior for MODE_DYNAMIC_LOCKED
(MODE_CHARACTER was forcing the body not to sleep, which is redundant
with can_sleep and wasn't done in Bullet).
