message: Add inverse_lerp()
diff: @@ -527,6 +527,13 @@ inline T lerp(T const& a, T const& b, T const& c, S const& u, S const& v)
  return s1 + s2 + s3;
  }
  +template <typename T, typename S>
  +MATH_FUNC
  +inline T inverse_lerp(T const& a, T const& b, S const& x)
  +{
  + return (T(x) - T(a)) / (b - a);
  +}
  +
  template <typename T>
  MATH_FUNC
  inline T step(T const& edge, T const& x)
  