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.
Check for each body individually if it collides with the other one or
ignores it.
When a body is being ignored, the other body's mass is considered
infinite when applying impulses to avoid extra overlapping.
New property disable_mode to set different behaviors:
Remove: remove from physics simulation
MakeStatic: change body mode to static (doesn't affect area and soft body)
KeepActive: do nothing
Extra change:
Handle disable/enable node state with specific notifications, in order
to differentiate global pause from disabled nodes.
