Documents and simplifies syncing code (#738)

* Add duplication prevention to gossipsub

* Clean up topic logs

* Add content addressed messages for gossip

* Support BlocksByRange step parameter

* Add initial docs to syncing

* Adds documentation and simplify code in sync

* Remove unnecessary comment

* Fix fmt issue

* Add batch log to sync

beacon_node/eth2-libp2p/src/rpc/mod.rs

@@ -66,7 +66,7 @@ pub struct RPC<TSubstream> {
     /// Queue of events to processed.
     events: Vec<NetworkBehaviourAction<RPCEvent, RPCMessage>>,
     /// Pins the generic substream.
-    marker: PhantomData<(TSubstream)>,
+    marker: PhantomData<TSubstream>,
     /// Slog logger for RPC behaviour.
     log: slog::Logger,
 }