Flushed out the api template for uart0.
We still need to add support for the ringbuffer
and more uarts
Added usart putn function
Added preprocessor support for disabling uart0
Added basic buffered input for uart0
Renamed uart.c and uart.h to usart.c and usart.h
Added documentation for usart input functions
fixed wrong compare of  rb_pop status in usart0_getc
Added simple simple usart output buffer
Added documentation for usart print functions
Added support for usart1 in usart.h
Added usart1 support
Changed all usart dependend modules to use the new
usart module.
Added file wide documentation for usart and
formatted documentation in ringbuffer.h
Added test case for buffered io
No also the prototype for usart[n]_hasData is removed if
NO_USART[n]_BUFFERED_INPUT is defined
Found missing ; after oneline while loop.
Also Found that the entire buffered usart is bugged
and needs fixing
Disabled buffered usart input / output in Makefiles