gnrc_netreg: mbox and arbitrary callback support

boards/nucleo-f103: remove STDIO_UART definition

gnrc_netreg: introduce helper macro/function for entry init

drivers: add support for LPD8808 based LED stripes

boards: initial support for Nucleo f030 board

boards/native: set PORT to tap0

cbor: fix off-by-one error

Improve execution of static-tests

The board is using the default value, so no need to
redefine it...

Cortex-M MPU driver and pseudo-module for guarding against stack overflows

boards/nucleo-f103: set stdio uart to USB port by default

cpu/atmega_common: include time.h for time_t

cpu/stm32f103cb: generalize linkerscript

netstats_l2: cc2538 (and at86rf2xx fixes)

shell: exclude hl and stats from usage if module not present

triggers an exception during stack overflow,
but at a cost of 32-63 bytes of RAM per thread.

boards/nucleo-l1: removed deprecated GPIO config

make: remove trailing slash from BINDIR and APPDIR variables

`PORT` is unset if `netdev2_tap` is not in `USEMODULES`.
But unfortunately, `netdev2_tap` is set by boards/native/Makefile.dep
*after* `PORT` is set, so that `PORT` remains empty.

This commit breaks this circular dependency by checking for
`netdev_default` and `gnrc_netdev_default` instead.

Without this commit, `make term` throws an error for examples that
require a tap interface, when `PORT` is not explicitely given.

boards: add remote-revb

add missing Makefile.dep files to boards remote-pa, remote-reva, and
remote-revb, as introduced by #5891. Otherwise certain features are
not working, such as radio.