This reverts commit fb3c2b2b.

The reverted commit broke Clang compilation.

sys: refactor synchronous uart

tests/unittests: add stm32f3discovery to BOARD_INSUFFICIENT_MEMORY

travis: remove .travis.yml and build scripts

cpu/stm32f1: implement lpm + run without PLL

cpu/stm32(_common & f2): implement delay after RCC peripheral clock enable

cpu/saml21: removed unused saml21_periph.h

boards/avsextrem: fix u_int type in smb380 driver

drivers/bmp180: move bmp180 driver to saul auto init using the correct way

gnrc_priority_queue:  fix doxygen document.

example/microcoap_server: fix link local address

Implements workaround 1 (use __DSB()) proposed in the stm32 errata
It was possible to lose data when you configure a peripheral
right after enabling its clock

cpu/stm32x: unified PWM driver implementations

cpu/stm32f4: Add I2C low speed support to the stm32f4

cpu/sam0: structural clean-up for sam[dlr]21 CPUs

gnrc_pktbuf_static: fix #5748

as we do not build the periph drivers selectable currently,
the guard is triggered even for boards that do not have any
PWM defined and don't want to use it...

sys: fmt: fix scn_u32_dec() documentation

gnrc_netdev2_eth: check bytes_expected > 0

timex: more conversion macros