feat: support tuple structs

[joshmossas]

It would be cool if there was a way to support tuple struct so that something like this

#[derive(Exported)]
pub struct Email(pub String);

could became

{
  "type": "string"
}

[joshmossas]

Or maybe there's a different trait that could be made to indicate something is a wrapper around a primitive type? Then we basically implement some methods to extract the primitive value out of it?

IDK just thinking out loud