`libinput` output pipelines

[jleightcap]

as planned, the libinput outputs looks something like:

/usr/bin/wacom-xy
0
0
1000
1000

where the output values are x coordinate then y coordinate delimited by \n characters.

likewise a designed interface for button presses as in #3.

• [x] design where ASCII coordinates are converted to literal representation. some shell pipeline? a small C program?
• [x] design how libinput button design interacts with the C runtime. a simple proof of concept might be a C program that prints hello on button press.