[Feature Request] Add containers, types, mimetypes, and other for metadata files

[labrys]

.. for e.g. nfo, posters, banners, etc.

$ guessit "Treme.1x03.Right.Place,.Wrong.Time.HDTV.XviD-NoTV.poster.jpg"
For: Treme.1x03.Right.Place,.Wrong.Time.HDTV.XviD-NoTV.poster.jpg
GuessIt found: {
    "title": "Treme",
    "season": 1,
    "episode": 3,
    "episode_title": "Right Place, Wrong Time",
    "format": "HDTV",
    "video_codec": "XviD",
    "release_group": "NoTV",
    "container": "jpg",
    "mimetype": "image/jpeg",
    "type": "episodemeta"
    "other": "poster"
}