checks remianing bytes when writing message
use English comment
improve error logging
add Mandatory normative statements todo list
check message length
for now, remove needless files
start refactoring engine
improve comment
remove neeedless methods
WIP: refactoring engine

Momonga also provides MQTT server library. this refactoring improve extendability.

[deprecated] tcp_connection: as integrating connection struct.
[new] myconnection: comes from client/connection.
[new] handler.go: event based message handler.

NOTE: You know momonga API is under development. don't rely their API
signature. it may changed.