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
Document sixlowpan/error.h
Refactor mac.h
Make usage of IPHC configurable.
added callback registration for sixlowip
added callback for sixlowpan
Refactor lowpan.h [not done yet]