Process posts without media files

[TestPolygon]

I think it would be useful to have a flag to process posts that have no media files, instead of skipping them, in order to run postprocessors, or just write a JSON with --write-metadata.

In order to have ability to save some text information that was posted without attached image/video files.

[Twi-Hard]

This is super important to me. I hope something like this can happen.:)

[mikf]

"postprocessors": [{
    "name": "metadata",
    "event": "post",
    "filename": "{post_id}.json"
}]

is how this should be generally possible at the moment (with a fitting filename for each site).

• "event": "post" to write metadata for each post. The default "event": "file", which triggers for each individual file, doesn't work at all for posts without files or duplicates most data for posts with more than one file.
• "filename": "{post_id}.json" because there is no default filename format for posts, only individual files.

(for Twitter in particular: 724ca61)

[TestPolygon]

What's about to add support for mastodon if it would be not difficult? Currently the program queries only posts with media files.

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Also I don't like how it works with --download-archive. This post postprocessor runs every time while it can. While I would prefer rerun it only with --no-skip (--no-download) option.
Maybe also to save in the history archive also entries of the posts if there is the post postprocessor in the config file? Or it would have some problems with archive_fmt?

For example, I run a command (with --download-archive): the program has downloaded all media and post postprocessor created the related files with meta information.
Next I move the folder to other place.
Rerun the command.
Files are not redownloaded as expected, but post postprocessor created the new files while I expected the skipping of it.