wrong multiplication operator for quat

[abisxir]

Default implementation looks buggy in version 2.0.0:

import vmath

# Correct implementation
func mult(q, p: Quat): Quat =
    result.x =   p.x * q.w  + p.y * q.z - p.z * q.y + p.w * q.x
    result.y = -(p.x * q.z) + p.y * q.w + p.z * q.x + p.w * q.y
    result.z =   p.x * q.y  - p.y * q.x + p.z * q.w + p.w * q.z
    result.w = -(p.x * q.x) - p.y * q.y - p.z * q.z + p.w * q.w

let
  q1 = quat(1, 2, 3, 4) 
  q2 = quat(5, 6, 7, 8)

echo q1 * q2          # vec4(5.0, 12.0, 21.0, 32.0)
echo mult(q1, q2) # vec4(32.0, 32.0, 56.0, -6.0)