Add README to the project.
Updated: Add project to Sublime Text.
Updated: Initialise the Task3.cpp, with testing codes of templates
Updated: Added operator override and constructor to the class Message
-- Play around with the constructor and operator override. --
Updated: Add copy constructor and "-" operator to the class Message
Updated: Add "+" operator to Message, checked with the function of "add".
Notice: Briefly finish the task3, need to be optimised by STL or not?