[library] SerialCommands: easy command-based sketches

Currently nothing stops one from writing

LIGHT ON
LIGHT OFF

The command routine would just see " ON" and " OFF" instead of "ON" and "OFF".

But you got me thinking... I could just ignore the first char after the command, so it would appear as if a blank was required between the command identifier and its arguments. That would certainly make for more readable examples :slight_smile: