Feature request: Implement reflection matrix calculation

[mariob92]

Reflection matrices can be used to implement mirrors on arbitrary planes.

Implementation example, from one of my projects:

eq contains the plane equation coefficients.

template <typename T, glm::qualifier Q = glm::defaultp>
constexpr glm::tmat4x4<T, Q> make_reflection_matrix(const glm::tvec4<T, Q> &eq)
{
    return glm::tmat4x4<T, Q>(-2.0f * eq.x * eq.x + 1.0f, -2.0f * eq.x * eq.y, -2.0f * eq.x * eq.z, 0.0f,
                              -2.0f * eq.y * eq.x, -2.0f * eq.y * eq.y + 1.0f, -2.0f * eq.y * eq.z, 0.0f,
                              -2.0f * eq.z * eq.x, -2.0f * eq.z * eq.y, -2.0f * eq.z * eq.z + 1.0f, 0.0f,
                              -2.0f * eq.w * eq.x, -2.0f * eq.w * eq.y, -2.0f * eq.w * eq.z, 1.0f);
}