message: add inline attribute to indexing
diff: @@ -361,6 +361,7 @@ impl<'a, N: 'a> DenseVector<N> for &'a [N] {
  self.len()
  }
  + #[inline]
  fn index(&self, idx: usize) -> &N {
  &self[idx]
  }
  @@ -371,6 +372,7 @@ impl<N> DenseVector<N> for Vec<N> {
  self.len()
  }
  + #[inline]
  fn index(&self, idx: usize) -> &N {
  &self[idx]
  }
  @@ -381,6 +383,7 @@ impl<'a, N: 'a> DenseVector<N> for &'a Vec<N> {
  self.len()
  }
  + #[inline]
  fn index(&self, idx: usize) -> &N {
  &self[idx]
  }
  @@ -394,6 +397,7 @@ where
  self.shape()[0]
  }
  + #[inline]
  fn index(&self, idx: usize) -> &N {
  &self[[idx]]
  }
  