Feature conveyor strategy

[pelamfi]

Hi

Just a short note here explaining why this fork of your podcatcher exists.
Feel free to merge this or if there is something you would like changed before
you can merge, let me know.

I'm setting up Ubuntu HTPC to automatically download podcast episodes from
multiple feeds when I plug in my MP3 player.

I have decided that the best strategy for me is as follows:

• It should try to keep specified maximum of files on the device of each feed.
• It should download unlistened episodes only to replace the ones
  I manually deleted (ie. after I listened them.)
• It should prefer new episodes over older ones.

This can now be achieved by combining parameters --strategy conveyor and --files N.

Example:

./podcatcher --strategy conveyor --files 3 --size 2000 --dir ~/podcatcher-state --cachedir /media/MP3PLAYER/PODCASTS http://feeds.feedburner.com/se-radio?format=xml