Adds new properties and xorg.conf entries for setting the acceleration
function's points and step.
`AccelProfile` option can now accept `custom` value.
Add 4 new options which only apply when `AccelProfile` is `custom`:
- Add `AccelPointsFallback` option for setting the points of the
Fallback acceleration function. Points values are represented by a
space-separated list, e.g. "0.0 1.0 2.4 2.5".
- Add `AccelStepFallback` option for setting the step of the Fallback
acceleration function. When a step of 0.0 is provided,
libinput default Fallback acceleration function is used.
- Add `AccelPointsMotion` and `AccelStepMotion` options, which are
equivalent to `AccelPointsFallback` and `AccelStepFallback` options,
but apply to the Motion acceleration function.
See libinput documentation for a detailed explanation of custom
pointer acceleration.
