`clean-intermediates` should be done per board. Without this it only
tries to clean the default board.

drivers/at86rf233: extend doc for smart idle listening feautre

drivers/at86rf2xx: add smart idle listening feature

tests/hacl: Move from unittests to regular test

docker: Use system GIT_CACHE_DIR if available

tests/pkg_micro-ecc: blacklist wsn430 boards

sys/base64: api change (const + void*)

crypto/helper: Change equals arguments to const

drivers: Add support for tsl4531x visible light intensity sensor

SAUL read functionality implemented only, as described in
tsl4531x_saul.c.
This driver will work with SAUL in both low and high power modes,
with the startup mode configurable in tsl4531x_params.h.

The changes to the test correspond to the change in the API and design
of the driver, as described in the previous commit and in tsl4531x.h.

Changes include:
- Implementation of two power modes for the driver: low and high
- Redesign and API change to the description in tsl4531x.h
- Full documentation
- Changing file structure and implementation to fit best practices as
  described in
  https://github.com/RIOT-OS/RIOT/wiki/Guide%3A-Writing-a-device-driver-in-RIOT
- Including I2C addresses for the rest of the range

Missing README.

Missing run modes and power saving configurations, but otherwise
functional.

If GIT_CACHE_DIR is a directory make it available to docker.
This will allow using the system git_cache also in the docker container.

Currently the default value was set by `dist/tools/git/git-cache`.
This moves/duplicates the default value in the build system.

 make: process include and dep for external modules

 cpu/fe310: rtc depend on the rtt feature and hifive1 update

It demonstrates:

 * Adding a module with source code
 * Setting a header include directory
 * Adding dependences, which are evaluated before other modules dependencies

If the application compiles, everything is ok.

Process `Makefile.include` for external modules. It is included after the others
so it could overwrite some of the configuration if wanted.

Process `Makefile.dep` for external modules. It is included before the others so
it could be parsed before setting 'default' values to dependencies.

Test breaks on wsn430 boards with the node rebooting.

This must come becauso `micro-ecc` does not have 16b support.
I also blacklisted the other 16bits boards.

 * https://github.com/kmackay/micro-ecc/issues/96

[doc] links http -> https

sys/eepreg: EEPROM registration support (version 2)

doc/boards: move jiminy from wiki to RIOT repo

tests/heatshrink: move from unittests to regular test

This moves tests for the heatshrink package from unittests to a regular
test, which should help to decrease binary size of unittests.

cpu/esp8266: cpu frequency settings feature added

net/nanocoap: rename variable name 'class'

'class' is keyword in c++ and leads to conflicts

boards/wsn430*: fix doxygen grouping