start to modularize: leds.c
start to modularize: adc:init_AnalogIn()
start to modularize: clock:enable_clock()
start to modularize: usart:USART_asyncTX()
move ADC IRQHandler to adc.c
split-off state-machine specific interrupt code to IRQ hooks.
experiment with IRQ hook function pointers
move transmitting variable into usart.c
clock TIM3 IRQ Hook function
cleanup imports
cleanup usart.c and move transmitting=1 into USART_asyncTX
cleanup includes
add comments to headers