Some podcasts don't include a sortable date as the first thing in their episode title, which makes listening to them in order challenging if not impossible.

The date the item was posted is part of the RSS standard, so we should parse that and provide a new importfeed template option "itemdate".

(For the curious, I tried "itemid" thinking that might give me something close, but it doesn't. I used --template='${feedtitle}/${itemid}-${itemtitle}${extension}' and get:

    http___openmetalcast.com__p_1163-Open_Metalcast_Episode__93__Headless_Chicken.ogg

or

    http___www.folkalley.com_music_podcasts__name_2013_08_21_alleycast_6_13.mp3-Alleycast___06.13.mp3

that "works" but is ugly :)

Would love to be able to put a YYYYMMDD at the beginning and then the title.

> [[done]]; itempubdate will use form YYYY-MM-DD (or the raw date string
> if the feed does not use a parsable form). --[[Joey]]