Added code documentation in several places, and made sure all GPIO
definitions are used properly everywhere (no direct references to index
in PIN_MAP). Makes it much easier to understand the code. Still lots to
do though
More progress at using constants instead of hex values for various low
level chip commands
Merge branch 'devel' of https://github.com/Safecast/onyxfirmware into devel

Conflicts:
	firmware/main.cpp
Merge pull request #54 from elafargue/doc

merging, all looks good.