dimensioned::dim_lhs_mult!

macro_rules! dim_lhs_mult {
    ($t: ty) => (
        impl<D> Mul<Dim<D, $t>> for $t
            where D: Dimension {
                type Output = Dim<D, <$t as Mul>::Output>;
                #[inline]
                fn mul(self, rhs: Dim<D, $t>) -> Self::Output {
                    Dim( self * rhs.0, PhantomData )
                }
            }
        );
}

Scalar multiplication (with scalar on LHS)!