Function slerp 

pub fn slerp<T>(a: Quaternion<T>, b: Quaternion<T>, t: T) -> Quaternion<T>
where
    T: Float,

Slerp (Spherical linear interpolation)

Generate a Versor that interpolate the shortest path from a to b. The argument t (0 <= t <= 1) is the interpolation parameter.

The arguments a and b must be Versor.