Add Bézier curve support

[nefarius]

Found these two cool projects that could work in user-mode driver code since it's good ol' ANSI C:

• https://github.com/msteinbeck/tinyspline
  • TinySpline is a small, yet powerful library for interpolating, transforming, and querying arbitrary NURBS, B-Splines, and Bézier curves. The core of the library is written in ANSI C (C89) with a C++ wrapper for an object-oriented programming model.
• https://github.com/rxi/fe
  • A tiny, embeddable language implemented in ANSI C.

Feature idea: use those in conjunction to add scripting support to complex parameters like axis curve transformation (maybe even rumble strengths?) from lightweight user scripts which eliminate the need to recompile. For example; user provides curve properties via scripting language, driver only takes those parameters and calculates the curve and applies it to axis transformation.