message: Make sure serde test is executed
diff: #[cfg(feature = "serde")]
  -fn main() {
  +#[test]
  +fn serialize() {
  use sprs::{CsMat, CsVecI};
  let v = CsVecI::new(5, vec![0_i32, 2, 4], vec![1., 2., 3.]);
  let serialized = bincode::serialize(&v.view()).unwrap();
  