introduce helpful macros to work with bit fields + use PosObject to move stuff

Moving down is impossible right now in favor of stance switching. It will be replaced by gravity at some future time.
As soon as gravity arrives, jumping should be trivial. After that, DIVEKICK!

Stabbing with the joystick button is in planning, but not there yet, as is sword throwing.

Oh yeah, also some weird artifacts from PosObject/HMove. I seem to remember forum posts about strange behavior too close to the left edge...