Broadcast a message to all clients, then flush the connection

The client except is skipped and will not receive the message.

Property definitions

gamnit $ Server :: broadcast
	# Broadcast a `message` to all `clients`, then flush the connection
	#
	# The client `except` is skipped and will not receive the `message`.
	fun broadcast(message: Serializable, except: nullable RemoteClient)
	do
		for client in clients do if client != except then
			client.writer.serialize(message)
			client.socket.flush
		end
	end
lib/gamnit/network/server.nit:101,2--110,4