sys: add riotboot_hdr module

cpu/esp32: fix of adc_res_t

boards/nrf51dk: add initial support

Unittest for riotboot_hdr submodule. If successful, it must
print 4 successful tests.

riotboot_hdr enables to partition the internal flash memory
into "slots", each one with a header providing information
about the partition. The concept for now is limited to
firmware partitions, which are recognised by the riotboot
bootloader. In the future the concept might be extended to
represent other content.

Co-authored-by: Kaspar Schleiser <kaspar@schleiser.de>

kw2xrf: Don't use netdev_ieee802154_t for channel

tests: adapt embunit TEST_ASSERT_EQUAL_STRING

crypto: Poly1305 implementation

board/*/flash.sh: get file to flash from command line

boards/sodaq-sara-aff: Initial support

jlink: get flash and debug files from cli

drivers: sht3x temperature and humidity sensor

This modification changes the netdev::set function for the kw2xrf to not
propagate the NETOPT_CHANNEL to the generic netdev_ieee802154 code

board: NXP Kinetis USB-KW41Z IoT USB dongle

Tests are based on the tests vectors provided in RFC 7539

poly1305 implementation strongly based on
https://github.com/floodyberry/poly1305-donna

kinetis: LPUART: Compute oversampling rate at init

usb-kw41z: improve doc and sort module dependencies

core: condition variable implementation

lwip: bump to version v2.1.2

cpu/esp32/include/periph_cpu.h overrides the default definition of adc_res_t from periph/adc with a definition which contains only four resolution, two new resolutions and two resolutions defined by the default definition of adc_res_t. This gives compilation errors if an application uses other resolutions. According to the documentation, adc_sample should return -1 if the resolution is not supported. All other CPUs override adc_res_t either to add new resolutions or to mark resolutions as unsupported. But they all allow to use them at the interface. Therefore, esp32 overrides now the definition of adc_res_t with all resolutions that are defined by the default definition of adc_res_t and new platform specific resolutions. It returns -1 if a resolution is used in adc_sample that is not supported.

crypto/helper: Add secure wipe function

gnrc_netif_hdr: make input parameters constant

 pkg/nimble: Remove warning suppressions, add patches

ethernet: make input parameter const