Using Cereal visitor pattern
Removed all the temporary references to cereal in fixed header
Removed encode function from MqttFixedHeader
Getting rid of silly header in base class for MqttMessage
Getting ready to get rid of MqttFixedHeader constructor for bytes
Got rid of the MqttFixedHeader constructor that takes bytes
Got rid of the other MqttFixedHeader constructor
Wrote accept for MqttConnect
Wrote accept for MqttPublish but not using it properly yet
Removed Cereal constructor for connack
Simplified the way the factory creates MqttConnect messages
Only one call to cereal.reset in the factory
Easier creation of MqttPublish
Refactored MqttPublish
Added accept to MqttSubscribe
Added accept to MqttSuback
Changed MqttConnect.accept to postBlit
Deleted MqttConnack.accept
Changed accept in MqttPublish to postBlit
Changed accept in MqttSubscribe to postBlit