Add a missing constant in 'radio_tx_status_t' enum
Merge pull request #1239 from rousselk/radio-API-again

Add a missing constant in 'radio_tx_status_t' enum
cleanup licenses to fix #392
Merge pull request #1217 from thomaseichinger/YALF

boards: cpu: cleanup licenses to fix #392
sys:transceiver: fix some doxygen comments
Replaced old release notes with the current ones
sys: add utility functions for `struct tm`
Add `struct tm` utility "test"
Merge pull request #1247 from thomaseichinger/transceiver_doc

sys:transceiver: fix some doxygen comments
Merge pull request #1146 from Kijewski/struct-tm-utils

sys: add utility functions for `struct tm`
x86: allow concurrent download of newlib
tests: add `concurrent_compile_test.py`

We are always on the brick of a timeout on Travis CI. Let's use more
concurrency.