cpu/stm32f0: fixed hardfault indication
cpu/stm32f1: fix i2c master read for N>2 bytes

This fixes reading more than 2 bytes from the slave device.
In the current implementation the last byte was not read from
data register and the termination sequence buggy.
cpu/stm32f1: fix i2c read for N=2 bytes
Added a function for the slave to print received data.
core: make sched_runqueue public

Reverting b604832, because thread_yield() needs to access this
information.
core: move thread_yield*() to thread.[ch]

Although it might conceptionally rather belong to the scheduler, the
yield functions are prefixed with thread_ and thus, belong there.
boards/mbed_lpc1768: disable DEBUG by default

Set ENABLE_DEBUG from (1) to (0)
native: add and use callback type
rpl_udp: add non-routing hosts to example
Merge pull request #1898 from LudwigOrtmann/native_callback_t

native: add and use callback type
cpu/sam3x8e: fixes to timer driver

- renamed config variable
- placed thread_yield() correctly
cpu/sam3x8e: put PendSV IRQ to lowest prio
cpu/sam3x8e: added output to isr_hard_fault
cpu/sam3x8e: fixed style in startup.c
drivers/mq3: added driver for alcohol sensor
tests: added test for MQ-3 alcohol sensor driver
board/stm32f4discovery: added ADC feature
Merge pull request #1703 from haukepetersen/add_driver_mq3

drivers/mq3: added driver for MQ-3 alcohol sensor
Enable SPI for udoo boards
Merge pull request #1897 from PeterKietzmann/add_udoo_spi

boards/udoo: added peripheral SPI definitions