Support error return and out parameters in declare_class!

[madsmtm]

Add the equivalent of #276 and #277 to declare_class!.

Effectively the implementation is:

// Result<(), Id<NSError, Shared>> -> Bool
match res {
    Ok(()) => Bool::YES,
    Err(err) => {
        // Intentionally not objc_autoreleaseReturnValue, since the optimization that enables will not be able to kick in
        *__err_param = objc_autorelease(err);
        Bool::NO
    },
}

// Result<Id<T, O>, Id<NSError, Shared>> -> *mut T
match res {
    Ok(obj) => obj.release_according_to_memory_management_rules(sel), // See #282
    Err(err) => {
        // Intentionally not objc_autoreleaseReturnValue
        *__err_param = objc_autorelease(err);
        ptr::null_mut()
    },
}

See #277 (comment) for further ABI details.