removed debug printf
added core_panic handler for Cortex

This commit also introduces a new folder to be include for all Cortex platforms, providing architecture common functionality.
include the newly introduced cortex_common in CPU specific Makefiles
introduces an enum for panic codes
fixed timer for stm32f103rey6

Using just the four C&C registers from TIM2 for timer and taking in
account that the timer is only 16 bit.
Merge pull request #14 from OlegHahm/cortex_panic

Cortex panic
Merge pull request #13 from OlegHahm/stm32f103rey6_timer

stm32f103rey6: fix hwtimer
Merge pull request #16 from OlegHahm/syscall_gettimeofday

implement gettimeofday syscall using vtimer
uart irq handler and first fix for the PendSV handler
force the toolchain to link the USART IRQ handler
moved CPU functionality to according file

Some unrelated stuff was implemented in atom.c, which should only contain a single function.