Add a new option with a type of String.

		:param str name: The name of the option, how it will be referenced.
		:param str help: The string returned as help to describe how the option is used.
		:param bool required: Whether to require that this option be set or not.
		:param str default: The default value for this option. If required is True and the user must specify it, set to anything but None.

def add_string(self, name, help, required=True, default=None):
		"""
		Add a new option with a type of String.

		:param str name: The name of the option, how it will be referenced.
		:param str help: The string returned as help to describe how the option is used.
		:param bool required: Whether to require that this option be set or not.
		:param str default: The default value for this option. If required is True and the user must specify it, set to anything but None.
		"""
		self._options[name] = Option(name, 'str', help, required, default=default)