ETA/OS 0.1.0-rc2

Signed-off-by: Michel Megens <dev@michelmegens.net>
irq: doc: added documentation to threaded IRQ code

All code supporting threaded IRQ's is now documented using doxygen.

Signed-off-by: Michel Megens <dev@michelmegens.net>
dev: usart: added docs to the usart drivers.

Added comments (aka documentation) to these drivers:

	* USART core driver
	* ATmega USART driver

Still need generic documentation for the USART (i.e. how to write to one
from an application).

Signed-off-by: Michel Megens <dev@michelmegens.net>