Replace (or augment) Math.scale with Math.lerp/unlerp (possibly with better names)

[thomcc]

Names obviously can be bikeshedded over to infinity, I'll admit that lerp/unlerp are bad ones. (GLSL goes with mix, HLSL goes with lerp, i've seen packages do linearInterpolate or interpolate and inverseLinearInterpolate, etc -- although those seem much too verbose to me).

Anyway, it seems extremely likely to me that linear interpolation is more common than linear remapping, and so a lerp/unlerp pair would get more use than Math.scale (even if they can be implemented by passing 0 and 1 as lo/hi values for Math.scale).

Including all 3 would be fine by me as well.

(P.S. other than that I'd like to thank you for including RAD_PER_DEG/DEG_PER_RAD as a constant in addition to a function!)