Parsing of the command

[eric-vader]

Commands supported:

• add: Adds a task to the task manager. It can add floating task #38 , deadline task #37 , timed task #21 , recurring deadline task or recurring timed task. #70
• alias: List all the aliases in the database.#65
• alias-add: Adds a new alias to the database.#69
• alias-delete: Deletes a alias from the database.#69
• delete: Deletes a task and moves it to the tasks recycle bin. #20 #66
• done: Done command is run when the task is completed.#66
• exit: Exits the task manager.#65
• history: Displays the current history of actions. #6 #65
• history-clear: Clears one, a range or all history. #68
• history-undo: Undo one history action. #11 #68
• modify: Modifies the task specified, updating the details of the tasks. #19 #70
• search: Search for a particular task in the task manager. #25 #70
• view: Lists the tasks in the task manager, giving the option to display in different formats. #12 #36
• help: Display help messages. #43 #65

[linchenhsin]

@rodsonchue Please write the the erroneous and the extreme test cases for Command.