Re: Use discogs as fallback if metal-archives don't work

[Chris Warburton]

I've added a check_on_discogs script. This currently:

 - Loops through artist directories
 - Strips country codes out of the directory names
 - Searches for the resulting artist name on discogs (with a 3 second delay to
   keep per-IP accesses below 25 per minute, and a unique user-agent)
 - Stores the resulting search pages into a cache
 - Attempts to find a correct discogs artist ID by looking through results for:
   - An exact match with the artist name (lowercased, alphabetical-only)
   - Results containing, or contained in, the artist name (lowercased, etc.)
 - If one exact match is found, or one fuzzy match, that's returned
 - Otherwise we error-out (and try/catch on to the next artist)

Still left to do:

 - Allow exact artist IDs to be given by an override file
 - Look up albums for an artist ID (via discogs API)
 - Look up tracks for an album
 - Check these discogs caches when checking for missing albums
 - Check these discogs caches when checking for missing tracks