Change description to reflect the configurability of the serial
interface.

Also, fix the uart_mode parameter description as the UART will be
configured and not initialized.

Signed-off-by: Yegor Yefremov <yegorslists@googlemail.com>

atmega: refactor cpu/board code and build/flash variables

sys/ps: Fixed stringification

makefiles/toolchain: fix command -v multiple commands

drivers/bmx280: fix dead links

URLs have been changed to:

https://ae-bst.resource.bosch.com/media/_tech/media/datasheets/BST-BMP280-DS001.pdf
https://ae-bst.resource.bosch.com/media/_tech/media/datasheets/BST-BME280-DS002.pdf

)

Signed-off-by: Yegor Yefremov <yegorslists@googlemail.com>

Added missing string for STATUS_COND_BLOCKED, so that the shell command "ps"
no longer crashes when a thread has this state.

cpu/esp8266: removes netstats in esp wifi netdev driver

kinetis: add support for S9KEAZ128

boards/sodaq-autonomo: switch to flashing with bossac

drivers: add support for SHT2x (I2C temp and humidity sensor)

cpu/stm32_common: fix UART documentation

gnrc: nib: fix DOXYGE -> DOXYGEN typo

Don't include overridden typedefs into doxygen as otherwise,
they'll appear twice.

Signed-off-by: Yegor Yefremov <yegorslists@googlemail.com>

Several parts were inspired by a driver written by:
  George Psimenos (gp7g14@soton.ac.uk)
  Steffen Robertz (steffen.robertz@rwth-aachen.de)

cpu/esp32: GPIO macro cleanup in periph_cpu.h

gnrc_sixlowpan_iphc: fix _compressible()

tests/gnrc_tcp_*: remove default PORT for native

Features must be provided by the board if they're actually
available on board. Other features might be provided by the
CPU.

Some grouping is also removed as it is not necessary.

Additionally, it removes unnecessary exports and cleans up
waspmote-pro toolchain variables (not needed) which are taken
from atmega_common.

Leverages common flasher (avrdude) and removes unnecessary exports.
Moreover, a reuse of serial.inc.mk is perfomed from the same
atmega_common/Makefile.include

Everything is now defined in atmega.inc.mk, following the common
RIOT-like reusability of rules and variables (e.g. cortexm.inc.mk).

Allows to use avrdude as a flashing tool in any context
(e.g. not dependent on arduino or atmega) though it only
works (AFAIK) on atmega, but I thought it's better to
have it here as we have other flashing tools.

shell_commands: adapt ping6 to original-ping-like implementation

drivers/w5100: Fixed netdev_driver_t::recv() API

When either `gnrc_sixlowpan_iphc_nhc` or `gnrc_udp` is not compiled
in `_compressible()` never returns `true`. This causes the
`dispatch` snip in `gnrc_sixlowpan_iphc_send()` to be of length 0,
meaning `dispatch->data` is `NULL`, causing possible crashes when
trying to send IPv6 packets over 6LoWPAN without NHC or UDP.

cpu/fe310: Add call to periph_init()

sam0_common: check ADC_NUMOF on adc_init()

cpu/sam0_common: update README for SAML1x addition

The default macros GPIO_PIN and GPIO_UNDEF do not have to be overridden. The GPIO_PIN macro definition was even wrong for 40 GPIOs without splitting into ports, even if that did not lead to erroneous behavior.

Fix hdc1000 renew interval documentation

chacha20poly1305: Initial implementation of AEAD cipher.

Loosely based on [the original ping] and [netutil]'s ping

New features (compared to old RIOT version):
 - non-positional parameters
 - Better duplicate detection (addresses #9387)
 - Better asynchronous behavior
 - Potential for future move to `sock_ip`
 - (Optional) DNS-support
 - Multithreading-safe (in case shell-command handler gets called
   from multiple threads)

[the original ping]: http://ftp.arl.army.mil/~mike/ping.html
[netutil]: https://www.gnu.org/software/inetutils/

The documentation refers to the `HDC1000_PARAM_RENEW_INTERVAL` as
`HDC1000_RENEW_INTERVAL`.