Create Command.java
Create CatCommand.java
Create CdCommand.java
Create CpCommand.java
Create ExitCommand.java
Create LsCommand.java
Create MkdirCommand.java
Create MvCommand.java
Create PwdCommand.java
Create RmCommand.java
Create Utils.java
Update Shell.java
interface Command->abstract, global Path
improved parser
bugfixes
chekstyle
Shell
Command.minArgNumber, Command.enoughArguments()
Fix bug in coping to subfolder or parent folder (cp -r . test)
Command.toString(), Command.commandName