timer: Refine Doxygen comment blocks of various entities
timer.c: Remove comments describing the code itself
shift: Refine Doxygen comment blocks of various entities
shift.c: Remove comments describing the code itself
ports.h: Refine Doxygen comment block of various entities
ports.h: Update year within copyright notice
ldr: Refine Doxygen comment blocks of various entities
ldr.c: Remove code describing the code itself
main.h: Refine Doxygen comment blocks of various entities
main.h: Remove declaration of main_ISR()
main.h: Move configuration options into own file

As this file basically contains only global configuration switches, it makes
more sense to move them into its own file named config.h. This moves all of
the configuration options over into the new file and updates all references
to it.
Move F_CPU detection into main.c

As this has nothing to do with the actual configuration of the project itself,
it makes more sense to move this into the main.c file.
main.c: Refine Doxygen comment block of various entities
main.c: Remove unnecessary comments describing code itself