func Pure(x, y, z float64) Quaternion {
	return Quaternion{X: x, Y: y, Z: z}
}
Pure returns a new pure quaternion (no scalar part)
package quaternion
import (
	"math"
)
func New(w, x, y, z float64) Quaternion {
	return Quaternion{W: w, X: x, Y: y, Z: z}
}