(Overlay) Add basic analog support

This adds analog stick support to the overlay code.  It's activated by setting the key to either 'analog_left' or 'analog_right' and providing a radial type hit box.

    overlay0_desc0 = "analog_left,94,385,radial,84,84"

The math still needs to be tweaked. Right now full movement maps right at the edge of the hit box, but there should probably be some buffer there to make it less likely to move your finger out of the analog area.