Adapt I2C interface to new coding style.

startSync -> startBlocking.
Add new SPI interface.

SimpleSpi without resource management, and
SpiMaster, SpiDelegate with resource management.
Peripheral: GPIO: Adapt AVR implementations to new coding style.
Add more documentation.
Peripheral: GPIO: Add Xmega PortConfiguration class.
Peripheral: Add i() method shortcuts to Xmega GPIO.
Core: Update coding style of AVR Core.
Perihperal: Update Coding style of I2C interface.
Update removal of GPIO defines from AVR examples.
Remove AVR interconnect example.