doxygen: remove x86-multiboot from excludes

nrf51: fix returns and error codes in periph/i2c

cpu, atmega_common: fix returns and error codes in periph/i2c

travis: enable static test in travis CI

at86rf2xx: fix channel asserts

tests: migrate simple tests to testrunner

boards/cpu: remove support for x86

dist/testbed-support: fix iotlab makefile indentation

sys/posix: factor inet_*to* from header into .c file

sys/net: add common lora phy definitions

tests/netstats_l2: migrate to testrunner

unittests: update boards lists

testrunner: make traceback extraction downwards-compatible

The object-like access to frame information in the traceback was only
introduced in Python 3.5. Before that version it was a 4-tuple [[1]].

The indexed way to access the frame seems to be upwards-compatible for
newer versions (tested with python 3.5, maybe some of the Arch crew can
test with even newer versions), so I used that one.

[1]: https://docs.python.org/3.4/library/traceback.html#traceback.extract_tb

tests/pkg_8g2: migrate to testrunner

cpu/nrf52: added ADC driver implementation