Creates new instance of Command.
Adds option
Adds command flag
Adds command argument
Registers subcommand
Command arguments
Gets command chain.
Command sub-commands
Sets default command.
Gets default command
Command flags
Sets command name
Program name
Command options
Sets program summary (one-liner)
Program summary
Sets command version
Program version
Represents a command.
Commands contain basic information such as name, version summary as well as flags, options, arguments and sub-commands.
Program is a Command as well, thus all methods are available in Program.