sbus is simple message bus based on unix domain, sequenced-packet sockets.

Features:
	Support for multi-user buses.
	No support state-keeping in clients.
	Supports all send(2)/recv(2) flags.
	Support for routing keys with wildcards.

Non-features:
	No IP or cluster support, should be implemented as a separate service.
	No support for overly larged messages, should be implemented at application level.
	No persistence support, should be implemented as a separate service.
	No support for automatic unsubscriptions.
	No support for reply-to keys, should be implemented at application level.
	No support for shared queues, should be implemented as a separate service.

Routing keys:
	Routing keys are used to filter received messages. A routing key
	may contain any byte, whoever there are two bytes with special
	meaning: '*' and '.'. '*' should not be used in routin keys, but
	only in routing key patterns, it matches until the next '.' or
	end if there are not more '.'s. Additionally if a routing key
	pattern ends with '.' that '.' will match to a '.' and any
	subsequent byte. For example 'a.*.c.' will match 'a.b.c.' and
	'a.b.c.d.e' but not 'a.b.c' or 'a.c.d'. And empty routiung key
	pattern shall match everything.

Protocol:
	Communication is done over unix domain, sequenced-packet sockets.
	Each packet is interpreted as a complete message. A packet cannot
	contain multiple message, and a message cannot be split over
	multiple packets. There are 3 types of messages:

	Subscribe:
		Send a routing key pattern to the server for the client.
		The server shall send all messages with matching routing
		keys to this client. The server shall store the key even
		if there is already an identical routing key pattern
		registered for the client.

		Messages of this type shall match the regular expression

			 ^SUB \([^\x00]*\)\(\x00.*\)\?$

		where \1 is the routing key pattern, \2 is ignored.

	Unsubscribe:
		Tell the server to remove a routing key pattern for the
		client. The server may choose to disconnect the client
		if it sends a routing key pattern that is not registered
		for the client.

		Messages of this type shall match the regular expression

			 ^UNSUB \([^\x00]*\)\(\x00.*\)\?$

		where \1 is the routing key pattern, \2 is ignored.

	Publish:
		Publish a message on the bus. The server shall send a
		copy of packet to all clients with a matching routing
		key pattern, including the client that sent the packet
		if and only if that client has a matching routing key
		pattern. The server may not send a copy of the packet
		to any clients without a matching routing key pattern.

		Messages of this type shall match the regular expression

			 ^MSG \([^\x00]*\)\x00\(.*\)$

		where \1 is the routing key for the message and \2
		is the message payload.