message: Add vector subtraction bound to EuclideanSpace
diff: @@ -310,6 +310,7 @@ pub trait EuclideanSpace: Copy + Clone where
  Self: Array<Element = <Self as EuclideanSpace>::Scalar>,
  Self: Add<<Self as EuclideanSpace>::Diff, Output = Self>,
  + Self: Sub<<Self as EuclideanSpace>::Diff, Output = Self>,
  Self: Sub<Self, Output = <Self as EuclideanSpace>::Diff>,
  Self: Mul<<Self as EuclideanSpace>::Scalar, Output = Self>,
  