Implement simple echo request/reply
Set up new directory structure
Move error codes to public includes
Make sixlowpan module more coding conventions compliant
Add documentation group for 6LoWPAN module
Update documentation of ipv6.h
Make usage of IPHC configurable.
added callback registration for sixlowip
added callback for sixlowpan
Refactor mac.h
Refactor lowpan.h
Refactor border.h
Refactor ip.h
Refactor icmp.h
Use new mutex API
Check if source address is not illegal source address.

Check if source address is not multicast or unique local unicast (for
non-local destinations.

Fixes issue #78
Don't note address operators as bit-wise and.

Fix https://github.com/authmillenon/RIOT/blob/3fddddd3be31a26684b21b1580f38c34cf2af81e/sys/net/rpl/rpl.c#L75
Fix typos
Make NCE type and status types publicly available
fix printfs in hwtimer_cpu.c