doc and code formatting update
- abstract docs (main page and all "Related Pages" now live in the docs folder)
- fix formatting
- some macros in RF24Network_config.h can be overridden from compiler CLI (using
-Dmacro_name=x
) or from project source code (before#include "RF24Network.h"
). These macros include:NETWORK_DEFAULT_ADDRESS
MAX_PAYLOAD_SIZE