WIP: marz: Initial commit

This adds a tool which can be used to reach RIOT nativenet instances
without a proper border router (for e.g. application layer testing).

It was useful for me, so I share it here (I do not think, that this necessarily belongs into the code tree, but you know why...)

TODOS:
(1) defragmentate 6LoWPAN
(2) add TCP
(3) cleanup the messy code
(4) rewrite the whole 6LoWPAN scapy module (it sucks)
(5) abolish python.