* Adding --help-json to get JSON encoded help message

This adds the `--help-json` flag which prints the help information
encoded in a JSON object. This enables template engines to render
the help information in other formats such as markdown.

* Adding --help-json to get JSON encoded help message

This adds the `--help-json` flag which prints the help information
encoded in a JSON object. This enables template engines to render
the help information in other formats such as markdown.

* Adding --help-json to get JSON encoded help message

This adds the `--help-json` flag which prints the help information
encoded in a JSON object. This enables template engines to render
the help information in other formats such as markdown.

* Adding --help-json to get JSON encoded help message

This adds the `--help-json` flag which prints the help information
encoded in a JSON object. This enables template engines to render
the help information in other formats such as markdown.

* Adding --help-json to get JSON encoded help message

This adds the `--help-json` flag which prints the help information
encoded in a JSON object. This enables template engines to render
the help information in other formats such as markdown.

This adds the `--help-json` flag which prints the help information
encoded in a JSON object. This enables template engines to render
the help information in other formats such as markdown.

* Adding --help-json to get JSON encoded help message

This adds the `--help-json` flag which prints the help information
encoded in a JSON object. This enables template engines to render
the help information in other formats such as markdown.

* Adding --help-json to get JSON encoded help message

This adds the `--help-json` flag which prints the help information
encoded in a JSON object. This enables template engines to render
the help information in other formats such as markdown.

* Adding --help-json to get JSON encoded help message

This adds the `--help-json` flag which prints the help information
encoded in a JSON object. This enables template engines to render
the help information in other formats such as markdown.

* Adding --help-json to get JSON encoded help message

This adds the `--help-json` flag which prints the help information
encoded in a JSON object. This enables template engines to render
the help information in other formats such as markdown.

* Adding --help-json to get JSON encoded help message

This adds the `--help-json` flag which prints the help information
encoded in a JSON object. This enables template engines to render
the help information in other formats such as markdown.

This adds the `--help-json` flag which prints the help information
encoded in a JSON object. This enables template engines to render
the help information in other formats such as markdown.

This adds 2 methods to arghm, help_json_from_args() and
help_json(), which is parallel to ::from_env().

The return value is a JSON encoded string suitable for
parsing and using as input to generate reference docs.

This adds 2 methods to arghm, help_json_from_args() and
help_json(), which is parallel to ::from_env().

The return value is a JSON encoded string suitable for
parsing and using as input to generate reference docs.

These were made inadvertently when merging changes.

This makes several changes that make it easier to use the JSON
help data and also makes it more complete.

* The subcommands are recursively called to collect the help information
  for each command. This means one call to help_json_from_args on the
  "TopLevel" struct will generate complete help for all subcommands.
* `options` has been renamed to `flags`.
* optionality has been added to the flags. This is "required",
  "optional", "repeated", or a Rust fragment containing for the default
  value.
* "arg_name" as been added to flags.

This also adds a default implementation of help_json_from_args for
FromArgs in order to be backwards compatible with non `derived`
implmentations of the FromArgs trait.