Improve acceleration curve / smoothing options

[1j01]

• Should be able to smooth out the jitter that occurs with your head standing still, without affecting the linearity of further (i.e. real) movement too much, at least if you don't want to.
• Should be able to make smooth circular movements. Right now it comes out kinda squarish. (Head tracking circularity: balance diagonal movement with horizontal/vertical movement #46)
• Can look at eViacam source code for reference, and play around with different algorithms.
• It's probably worth it to add a serious curve editing UI, in order to find what works, and then distill that into a simple control. Can use @mojs/curve-editor.
• Minimum distance to start moving pointer (option) — I don't know how much different this would be from configuring the acceleration curve, but it could help.

[1j01]

eViacam actually has separate options "Smoothing" and "Acceleration" (in addition to "Easy Stop", which is easier to understand).
I'm not sure what the distinction is, but Smoothing seems to be mapped to a "low pass filter":

• GetSmoothness and SetSmoothness in pointeraction.h

whereas the Acceleration uses a discrete set of configurations using differing numbers of default parameters to a function:

• CPointerAction::SetAcceleration in pointeraction.cpp
• CMouseControl::SetRelAcceleration2 in mousecontrol.cpp