Feature Request: targets tag --append-tag variant to add a tag to an existing target

[mike-scott]

There can be issues when using targets tag <target list> -T <tag>,<tag> to ADD a tag to a target.

If you aren't careful, a copy/paste error can move a target from it's original tag to something else when you're trying to preserve that original tag while adding a new one. The original syntax requires more knowledge about the target than it should to just add a tag.

[mike-scott]

Also related: #102