Middleware alias for middleware_fn

[ynuwenhof]

Proc macro attribute alias for #[middleware_fn].

#[middleware]
async fn alias(mut context: Ctx, _next: MiddlewareNext<Ctx>) -> MiddlewareResult<Ctx> {
    let val = "Hello, World!";
    context.body(val);
    Ok(context)
}

#[middleware_fn]
async fn original(mut context: Ctx, _next: MiddlewareNext<Ctx>) -> MiddlewareResult<Ctx> {
    let val = "Hello, World!";
    context.body(val);
    Ok(context)
}