ng_ipv6: initial import

pktbuf: clarify doc of pktbuf_add()

rpl: remove unnecessary check for multiple instances

shell: sc_netif: add set/unset for flags

Fixes #2853

net/ng_netconf: added option for setting RAW mode

Yet another doxygen fix

pkg: added information about creating a patch

doxygen: generate graphs for includes

* sixlowpan doxygen group does not yet exist

unittests: move netreg entries out of stack space

Fix unaligned access on Samr21/Cortex-M0

drivers/xbee: misc fixes 

Add fix for clockid_t on OS X

Tests : Add missing Makefile and Makefile.include for tests-hash_string

- fixed sending of with long addresses
- corrected type setting of netif hdr pktsnips

unittests: fix and unify header guards

- Adds the missing files from #2793.

ng_sixlowpan: initial import of a context buffer

Use transceiver specific broadcast

ipv6_addr: add missing mask to prefix initialization

Tests: Fixing warnings in hash_string_module

pktdump: fix formatting of snips and false illegal version warning

ps: fix module prefix and documentation plus minor cleanup