motor: Avoid using integer division

Atmel AVR does not have a divide instruction, and division is generally slow
anyway.

Signed-off-by: Morten Hustveit <morten.hustveit@gmail.com>
Simplify run-time arithmetic in baud calculations

Arduino doesn't have a divisor, so by completely avoiding divison we can
properly generated warnings if division is accidentally re-added to the code.

Signed-off-by: Morten Hustveit <morten.hustveit@gmail.com>
Merge branch 'master' of github.com:mortehu/motor

Conflicts:
	main.cc
	serial.h
	serial_arduino.c
	serial_uno32.c