Note: completely untested. It merely compiles
This patch adds support for the new custom pointer acceleration method in libinput, see libinput/libinput!775 (merged).
Adds new properties and xorg.conf entries for setting points and the step.
cc @Yinon, this should be most of the integration into the driver. It's just quickly typed out and untested though, so it's likely to crash the server. Plus, it needs a good look to see if it all makes sense and can actually work. Also, the man page entries are missing and the commit message is a bit short... If you could take this over that'd be great.