added support for the ADC module of the mc1322x MCU
adjusted default stack sizes for msp430

* stack size for idle thread was too small
* main stack gets initialized with KERNEL_CONF_STACKSIZE_DEFAULT +
  KERNEL_CONF_STACKSIZE_PRINTF, leading to a huge main thread stack
moved GPIO implementation from boards to RIOT since ADC implementation depends on it
Merge pull request #174 from thomaseichinger/ADC

ADC module of the mc1322x MCU
Merge pull request #215 from OlegHahm/msp430-stack_sizes

adjusted default stack sizes for msp430