Switch absMouse to a coordinate system with an origin of 0,0 in the upper left
corner, rather than the center of the screen.

Allowing negative absolute coordinates leads to hard-to-debug problems with
overflow and 'unreachable' parts of the screen.
Remove mouse wheel support from moveAbs.

There's not a lot of value to having there be two ways to move the
mouse wheel from two different (but similar) APIs.

Additionally, with the change to zero-origin for absMouse,
the zero-point for the wheel gets a little bit more confusing for users.