avrdude.mk and serial.mk was included twice. As a result of the former, avrdude
wasted one flash cycle and some time by writing the same firmware twice.
Every ATmega board that can run an Real Time Timer can also run
an emulated Real Time Clock.
Got all supported boards by adding `FEATURES_REQUIRED += arch_8bit`
to `tests/periph_rtt` and running
sed -i 's/FEATURES_PROVIDED += periph_rtt/
FEATURES_PROVIDED += periph_rtc\n
FEATURES_PROVIDED += periph_rtt/g'
on them.
- Using @warning Doxygen command to make warning more visible
- Used IEC units for size specifications
- Aligned markdown source of the table
- Added note that the 5V pin is not connected to the board and cannot be used
to power the board
