- Allowed a coderef to be passed as default in add_arguments()
- Initialised current_command() for namespace at parse_args() to fix
  'unknown option' bug
- Checked if current_command exists
- Fixed an error in default check
- Removed executing coderef for default
fixed current_parser not initialized
added add_arg and add_args method for consistency
Updated perldoc
added aliases to Parser for subparsers
updated for release 1.0.1
Updated MANIFEST