drivers: Initial import of SPI low-level driver IF
drivers: fixes to the SPI low-level interface
driver: updated SPI driver interface
[SQUASH ME] added fixed speed values
[SQUASH ME] removed UNDEFINED from device list
[SQUASH ME] fixed signature of spi_transfer_reg()
[SQUASH ME] added begin_transaction, fixed doc
make: force traversal into PKG's, same as normal modules
cpu/board: added ADC driver for stm32f0discovery

- added ADC implementation for the stm32f0 cpu
- added ADC pin/device configuration for stm32f0discovery board
cpu/board: added ADC driver for stm32f4discovery
lpc2387: change comment style for license checker
lpc2k: unify Paul Stoffregen license headers
Merge pull request #1314 from LudwigOrtmann/license_unification

License unification
cpu/cortex-mX_common: fixed type issues

- added explicit cast for stack pointer
- fixed printf type inconsistency
cpu: Initial import of stm32f3
board: Initial import of stm32f3discovery
cpu - cortex-m4_common: fixes to thread_arch.c
examples/tests: blacklisted stm32f3discovery
Implement CPU serial number getter.
converting tabs to spaces in boards (#1439)

This PR converts tabs to white spaces.
The statement I used for the conversion:
'''find . -name "*.[ch]" -exec zsh -c 'expand -t 4 "$0" > /tmp/e && mv /tmp/e "$0"' {} \;'''
Afterwards, I had a quick overview of the converted files to prevent odd indentation.