libei and graphics tablets stylus support

While you (yes, you! no, not you, the one behind you) have been sweltering in the heatwaves of the northern hemispheres (Assisted-by: AI), I've been busy adding graphics tablet support to libei. This is scheduled for the soon to be released libei 1.7.0. The initial work was done by Jason Gerecke and Josh Dickens from Wacom, I've been extending, polishing and testing it for the last few weeks.…