1.6.0 - add optional serde implementations

The bytes to key parsing in Termion is super useful and something we need in Zellij, but we also need to Serialise things occasionally!

Rust's orphan rule makes this a massive pain normally, so we needed a fork to derive it.

This adds Serialize and Deserialize implementations to some input structs when the serde feature is enabled. It shouldn't have any affect at all when the feature is off (as is the default).