add new functions to play tag, track or album, and fix a couple of minor bugs

[MonkeysAreEvil]

• Add arguments to play either a track, tag, or album
• Update bandcamp_parser.Album.tracks() to eliminate duplicate tracks returned by the parser
• Update bandcamp_parser.Track.download_link() to raise an error when bandcamp does not provide a valid file.

[MonkeysAreEvil]

Yeah fair enough about argparse just being lazy. I can push an update to that when I get a spare minute. And I'll check the download link too --- I haven't had any issues yet with that.

[MonkeysAreEvil]

Ok so, busy week, but have a moment now to look at this again. I've updated to use argparse, so that's a little cleaner now.

The reason I added a check to download_link is because when Bandcamp fails to produce an mp3 the exception thrown is quite long and I doesn't tell you what's gone wrong. It's only happened a couple of times and I can't reproduce it at the moment, but I recall that the exception given suggests that there's an issue with soup not with the content Bandcamp returned. I think it's a little easier to understand what's gone wrong here by throwing a more specific error.