Add error checking in mailbox send

This function now raise a meaningful error when non-mailboxes are passed in.
Document radio.js using radio.md
Change smart sensor -> smart device in documentation.
Update smartdevice.txt to use 2x5 header.
New radio protocol YAML file copied from Daemon
Clean up unused printf handling radio code
Change setGameMode to a public function
Merge remote-tracking branch 'upstream/master'