pkg: u8g2: improvements and bugfixes

sys/ecc/hamming256: fix variableScope (cppcheck)

This matches better with other tests and makes code less bloated.

New version introduces better support for the different SPI modes.

pkg/nordic_softdevice_ble: gnrc_nordic_ble_6lowpan: fix nullPointer error (cppcheck)

tests/xtimer_now64_continuity: fix variableScope (cppcheck)

tests/periph_uart: fix invalidPrintfArgType_sint (cppcheck)

pkg/emb6: emb6_conn_udp: fix nullPointer error (cppcheck)

tests/driver_dht: fix invalidPrintfArgType_sint (cppcheck)

sys/net/gnrc: fix cppcheck errors/ warnings

drivers/dht: fix variableScope (cppcheck)

sys/base64: fix variableScope (cppcheck)

Since the argument type is 'unsigned int', the printf
format string has to be '%u' instead of '%i'.

Since the argument type is 'unsigned int', the printf
format string has to be '%u' instead of '%i'.

cpu/cc2538: Make ED and LQI values 802.15.4 compliant

at86rf2xx: document operation mode concerns for

at86rf2xx: at86rf2xx_get_random to at86rf2xx_internal for supporting boards

csma_sender: fixes and adaptions

Works for at86rf233 and at86rf231 chips

gnrc ipv6: convenient function to get the header

fix sys/crypto header include guards.

Fix sys/embunit header include guards.

Include tiny-asn1 as a package

cpu: add stm32f2xx family support (based on #4497)

cpu/atmega_common: improve to add smaller atmega MCUs.

dist/tools: update serial boot loader script