Is there any way to list all of the existing tag and metadata field types? What I mean is, I have files tagged with several different tags, files with several metadata fields; is there any way to list all the tag and field names being used (not all the files WITH those tags)?

For example, something like:

    git annex metadata --listfields
    lastchanged
    month
    month-lastchanged
    year
    year-lastchanged

    git annex metadata --listtags
    Public
    Personal
    Work
