Monocypher: Initial import of package

gnrc_sixlowpan_frag: add current_size to exposed struct

Support for monocypher as crypto library. Blazing fast performance, but
double the flash requirement compared to TweetNaCl. Stack usage is
around 70% of TweetNaCl

boards/iotlab-m3|a8: fix openocd configuration

iotlab-m3 boards always ended up not being able to flash after time.
This changes managed to fix and flash boards that where able to be flashed with
the deprecated `ft2232` driver and not with the `ftdi` driver used in RIOT.

It combines configuration from openocd, iot-lab, RIOT config and Alexandre
Abadie feedback

* http://repo.or.cz/openocd.git/blob/HEAD:/tcl/interface/ftdi/iotlab-usb.cfg
  * ftdi configuration
* https://github.com/iot-lab/iot-lab-gateway/blob/2.4.1/gateway_code/static/iot-lab-m3.cfg
  * `trst_and_srst` config
* Alexandre feedback and http://openocd.org/doc/html/Reset-Configuration.html
  * 'connect_assert_srst' reset configuration
    * it prevents errors in the output on first flash
    * should help on boards with invalid code
    * It was taken from what Alexandre found for board 'b-l072z-lrwan1'
  * It requires using '-c reset halt' instead of '-c halt' before debug
* RIOT
  * Keep the `configure -rtos` auto

tools/mkconstfs: Add an improved tool.

The new tool (mkconstfs2) features:

* more robust filename handling: no need for mangling,
  and works on Windows.
* Better output generation: nothing is written in case
  of failures.
* Allows more control over the files that are included:
 - does not traverse directories, filenames must be explicitly
   given.
 - The "root" can be explicitly given (thus the tool can get
   the same result independently of the CWD).

Thanks to MichelRottleuthner for making it work with Windows paths.

boards/mulle: Fix mixed up RX TX pins on UART0

pkg/jerryscript: update to latest commit

boards/b-l072z-lrwan1: fix openocd configuration and 'make debug'

drivers/pn532: fix wrong buffer type

cpu/stm32f2: make use of CPU_LINE

cpu/stm32f3: make use of CPU_LINE

cpu/stm32f7: make use of CPU_LINE

cpu/atmega_common: misc gpio interrupt fixes

cpu/atmega_common: Use updated time.h

net/nanocoap: test coap_get_uri() boundaries

gnrc_sock_udp: use sock's local end-point for listening

Without this fix the listener doesn't actually listen on the
(potentially) ephemeral port introduced in #9382, but on port 0 which is
wrong.

boards/stm32: use common place of openocd config files for all boards using stlink

make: add and export RIOTTOOLS directory

Add newly added tests

doc: add requirement for two acks for changes

Since IPHC also manipulates the total number of bytes of a received
datagram (by decompressing it), this also needs to be exposed. I guess
I was too focused on introducing a *generic* packet buffer for a future
virtual reassembly buffer (where it isn't needed, but so isn't `pkt` to
be honest), that I totally forgot about it in #9352.

- Two ACKs should be required to ensure that the maintainer guidelines
  remain credible.

doc: Add atomicity to review fundamentals

drivers/lis3dh: apply unified driver params scheme + cleanup

kinetis: Clean up SPI module power handling