changed parameters form `kernel_pid_t` to `int`
core: introduce KERNEL_PID_FIRST and KERNEL_PID_LAST
core: let valid PIDs start with 1
examples: renamed rpl_udp header
examples: cleanup for rpl_udp

* removed unnecessary shell commands
* updated documentation
* Unified global default IP address
rpl: moved headers to sys/net/include
examples: don't advertise IPv6 prefix

Cleaning up the IPv6 address initialization and removed the addition of
an IPv6 prefix to advertise.
examples: use correct broadcast address when sending
fix low-level sending destination address
licenses: updated some missing licenses in headers
boards:make: hardcode goodfet.bsl path in Makefile.include
goodfet: hardcode python version to 2.7
Merge pull request #1573 from thomaseichinger/hardcode_goodfet

boards:make: hardcode goodfet.bsl path in Makefile.include
cpu/nrf51822: added RTT driver implementation
board/pca10000: enabled RTT timer in periph_conf.h
ccnl: use correct packet type
Merge pull request #1566 from Kijewski/undef_is_null

core: let PIDs begin with 1
tests/periph_rtt: added test for RTT drivers
make: Fix TERMFLAGS

Sometimes boards/*/Makefile.include (e. g. in case of the msba2) gets included
twice somehow, leading the TERMFLAG to be set twice and faulty. This
fixes that.
Merge pull request #1554 from OlegHahm/rpl_udp_cleanup

examples: rpl_udp cleanup