Render an individual tiddler as a specified ContentType, defaulting to `text/html` and save it to the specified filename.
Optionally the title of a template tiddler can be specified, in which case the template tiddler is rendered with the "currentTiddler" variable set to the tiddler that is being rendered (the first parameter value).
A name and value for an additional variable may optionally also be specified.
By default, the filename is resolved relative to the `output` subdirectory of the edition directory. The `--output` command can be used to direct output to a different directory.
For example, the following command saves all tiddlers matching the filter `[tag[done]]` to a JSON file titled `output.json` by employing the core template `$:/core/templates/exporters/JsonFile`.