Add a `deprecated` parameter to click.Option and click.Argument, like the one Command already has. It accepts either a bool or a message string. When a deprecated parameter is given on the command line, print a warning to stderr (including the custom message when one is given) but still run the command; nothing is printed when the parameter is not used. Deprecated options show "(DEPRECATED)" plus the message, if any, in --help. A required parameter cannot be deprecated: raise ValueError when such a parameter is defined. Add tests and document the parameter, and run the full test suite with `python -m pytest` before you finish.
