Matrix serialization is length-delimited but deserialization isn't

[danielkeller]

For example, with bincode, the following assertion fails:

let unit = Mat4::identity();
assert_eq!(
    unit,
    bincode::deserialize::<Mat4>(&bincode::serialize(&unit).unwrap()).unwrap()
);

It looks like the serializer inserts a length that the deserializer doesn't read.

[AlphaModder]

This occurs because the Serialize impl calls serialize_seq but the Deserialize impl calls deserialize_tuple. ron is also affected. I have opened a PR #140 to fix this.