-** FIXME: get_pressure_multiplier() should access correct members
- of event struct, like xinput_coords()
-** FIX RECOGNIZER BUG: for single-segment strokes (e.g. single click),
- I_xx and I_yy = 0, sometimes -0 -> Rad = nan (should I_xx = abs(...) ?)
- also Det = division by 0, should return 0 if ixx + iyy = 0.
- (MAYBE: fix inertia calc: integrate dm over each segment rather than dm.pt[i])