Draft: Hex str or components

This is a better (but still non-functional) approach at using both component and hex-string colors.

I'm using a custom serde deserializer, unfortunatelly, it is not yet working. Leaving it here so maybe you have a better idea on how to proceed (i'm too tired to continue today).

Got my inspiration from:

• https://serde.rs/impl-deserializer.html
• https://serde.rs/deserialize-struct.html
• https://docs.serde.rs/serde/de/trait.Visitor.html

Errors we get

• We get an error when trying to parse a hex string: invalid type: string \"#0000ffff\", expected RgbaComponents
• We get an error because, even if RgbaComponets knows (eventually) how to deserialize itself from a string, the ColourDefinition Enum can't match the String representation and it does not know to which enum variation this color matches.