underlying hardware/mcu. Created avr_gpio.h to define AVR pin registers
in a struct fashion similar to what's common with ARM code. Doing that
makes things much easier to abstract in pin macro 'functions'.
Added define to Makefiles that flags pinport_al.h which board is targetted
for build.
Tested and able to turn on/off and pull-up LED on all 3 builds.
Paul Molloy