VovaDev

Added marshalledSize to all classes

2

Fixes #11. Implemented marshalledSize for all classes (like in [Java](https://github.com/open-dis/open-dis-java/tree/master) and [C#](https://github.com/open-dis/open-dis-csharp) implementations). You still need to manually fill pdu.length field (aka `pdu.length = pdu.marshalledSize()`), but at least you could...