pass_module interacts badly with pyfunction arguments

[davidhewitt]

At the moment pass_module can interact in confusing ways with pyfunction arguments - it can go in any position, which is a bit confusing:

#[pyfunction(a, b, args = "*", pass_module, d = "5")]
fn test_function(m: &PyModule, a: i32, b: i32, args: &PyTuple, d: i32) {
    println!("{}, {}, {:?}, {}", a, b, args, d)
}

... I'm working on a PR which will change the situation such that pass_module must go first, if present.