* drop support for v4 (obsolete, doesn't work with all clients since
they use chunking and other obsolete v4 features that we're missing or
don't support it at all)
* rework asyncraises
* always store generated p2p macro code (similar to eth2)
* preparation for chronos cancellation support (more to be done here)
* when peer is disconnected, ensure pending handshakes and requests are
notified (instead of waiting for timeout)
* disallow raising from `onPeerDisconnected` - this simplifies
disconnection coordination among async tasks
* introduce several warning logs for protocol breaches - these should be
removed eventually, pending q/a on the rlpx layer in general
* fix snappy compression - the payload without msgId should be
compressed
* remove strict checks on unused fields in RLPx message header (this
matches geth behavior and the spirit of EIP-8)
* add snappy dep
* disconnect peers that send non-hello messages during initial hello
step
* fix devp2p protocol version - 4 because we don't implement snappy
(yet) - this is cosmetic since this particular version field is not
actually being used
* fix ack message length checking
* move RLPx transport code to separate module, annotate with asyncraises
* increase max RLPx message size to 16mb, per EIP-706
* make sure both accept/connect timeout after 10s
* aim to log every connection attempt once at debug level
* make capability-id/context-id check more accurate
* disallow random messages before hello
Jacek Sieka