Manually implement serde::Serialize/Deserialize for bigger t values

[elichai]

We might want t that is bigger than 32, which will then break auto deriving serialize/deserialize because of serde-rs/serde#631.
I wanted to implement this myself, but the implementation gets very big and complex very fast (you need multiple types, and visitors, implementing traits for all of them etc.), instead I found that a common crate that allows you to do it: jonasbb/serde_with#272

[omershlo]

brilliant,
mandatory question: have you run the test with c=2 t=76?