* Avoid global in p2p macro (fixes#4578)
* copy p2p macro to this repo and start de-crufting it
* make protocol registration dynamic, removing light client hacks et al
* split out light client protocol into its own file
* cleanups
* Option -> Opt
* remove more cruft
* further split beacon_sync
this allows the light client to respond to peer metadata messages
without exposing the block sync protocol
* better protocol init
* "constant" protocol index
* avoid casts
* copyright
* move some discovery code to discovery
* avoid extraneous data copy when sending chunks
* remove redundant forkdigest field
* document how to connect to a specific peer
Jacek Sieka