Handle management messages instead of letting them bubble up through the
connection to the consumer.
Right now, this just means handling ping messages by sending a pong.
Also updated to follow the new handshake flow.
The sentinel will mirror the ports instead of matching them.
Now filters on the full source and dest ports, which are less likely to
have erroneous matches.
Also added networkBytesAsValue and restored bytesAsValue.
These are useful for treating the bytes from the network directly as a Message.
Otherwise, the init function would overwrite the packet type and length to be correct.
I would like the message handling to fail if the message body is incorrect.
The slice sets us avoid allocating within the init function.
This means init can't fail, and it also makes it easier to stack allocate messages (slice an array buffer, instead of creating a stack allocator).
