Hi!

First of all, thank you for this cool crate.

Recently I have worked on implementing support for the borsh crate to make it possible to derive its traits using nutype.
While working on it, I encountered the error that it is impossible to derive both serde and borsh traits.
This was because I used instance methods, and there was a conflict of serialize method implementations.
I solved this using the original trait method, and now everything works fine.

This little change is supposed to avoid such problems in future features.
Also, this will improve code consistency because such an approach is already used in the Deserialize trait implementation.

::serde::de::Deserializer::deserialize_newtype_struct(
    deserializer,
    #type_name_str,
    __Visitor {
        marker: Default::default(),
        lifetime: Default::default(),
    }
)