Add with-serde feature

[Coffelius]

This feature derives the de/serializable traits in each of the command types.

Rust's orphan rule requires that either the trait or the type for which you are implementing the trait must be defined in the same crate as the impl, so it is not possible to implement Serialize and Deserialize for a type in a different crate directly.
https://serde.rs/remote-derive.html

However, even following the remote derive workarounds provided by Serde, it seems that there isn't yet a way to remote derive the structs that contain types nested in Option, Vec, or Map without having to write a lot of boilerplaty code that hard to keep synch with twitch-irc-rs updates.
serde-rs/serde#723

The reason why I need to serialize the commands is because I'm using an architecture in which all the mensajes obtained by twitch-irc-rs are relayed using a publisher pattern and proxy balanced, while there are subscribers that perform all specific logging and bot operations that can be disconnected or replaced.

Pull request checklist:

• [*] CHANGELOG.md was updated, if applicable

[RAnders00]

Thank you! I hope you don't mind that I made some changes...