Proposal: BodyParser Should Change Contract

[craftytrickster]

Currently body parser works by returning a Result<Option>:

    let struct_body = req.get::<bodyparser::Struct<MyStructure>>();
    match struct_body {
        Ok(Some(struct_body)) => println!("Parsed body:\n{:?}", struct_body),
        Ok(None) => println!("No body"),
        Err(err) => println!("Error: {:?}", err)
    }

I believe that adding an Option to the return type forces the consumer to have an extra level of matching for no gained benefit (in my personal opinion).

If I am trying to parse a body and there is no body present, I would argue that it should be an Err, instead of being Ok(None), after all, I was expected a value to be there that is missing. You can add MissingBody as a potential error code.

I believe this would simplify the API and make it easier to consume.

If the maintainers of this repo agree with my proposal, I can go ahead and submit a PR.

Thanks.