Standing ok, a bit wobbly
use prev CoM position to calculate CoM velocity
Stub of Featherstone stuff
Working really rather nice. steps backwards though.
. add knee out, knee up
. correct gravity compensation -/+ switch
. correct foot joint limits
walking nicely
Improvements to upper body pose, shoulder definitions (need to check
        impl. of conetwist)
Don't force-enable the cone-twist joint motors. Use fixed btFixedConstraint
from bullet rev 2719
Cleanup; make span actually mean span; good arm parameters
fix cone twist spans
Bring in more cartwheel stuff (panic, ankle crossing)
lots of param tweaks