Subcommand to edit existing torrent files

[casey]

• [ ] imdl torrent edit
• [ ] allow editing source files
• [ ] set info.entropy.
• [ ] Check out https://github.com/rndusr/torf-cli for inspiration
• [ ] --dry-run to show what would be done
• [ ] --clean to remove nonstandard metadata
• [ ] --anonymize remove anything that might be identifiable
• [ ] --public and --private to change private flag

A great first stab at this would be to add the subcommand, and add the ability to set the source of a torrent, with something like:

$ imdl torrent edit --input foo.torrent --set source foo

Setting the source of a torrent is likely to be one of the main uses of editing torrents, so it's a good place to start.

I'd like this to use a relatively small number of generic flags:

• --set NAME VALUE set the given named field to VALUE. NAME should be the name of a field, not a path, so info.source should be set with --set source FOO.
• --remove NAME remove the given field, if set
• --update NAME add or update a field that has a default, like created by, or creation time

Ideally, the same flags should also be accepted by imdl torrent create and imdl torrent link

[wally-crunk]

Adding a ''source tag'' edit function to intermodal would be very nice.

The tools I've tried that can do this have been problematic. [Won't install; hokey UI; etc.]