A second base class, LibModel, maintains a reference to the Library and should
take care of database-related tasks like load and store. This is the beginning
of the end of the terrible incongruity between Item and Album objects (only
the latter had a library reference). More refactoring to come.
One large side effect: Album objects no longer automatically store
modifications. You have to call album.store(). Several places in the code
assume otherwise; they need cleaning up.
ResultIterator is now polymorphic (it takes a type parameter, which must be a
subclass of LibModel).
In preparation for enabling queries over flexattrs, this is a new path that
lets queries avoid generating SQLite expressions altogether. Any query that
can be completely evaluated in SQLite will be, but when it can't, we now fall
back to running the entire query in Python by selecting everything from the
database and running the `match` predicate.
To begin with, this mechanism replaces RegisteredFieldQueries, which
previously used Python callbacks for evaluation. Now they just indicate that
they're slow queries and the query system falls back automatically.
This has the great upside that it lets use implement arbitrarily complex
queries without shoehorning everything into SQLite when that (a) is way too
complicated and (b) doesn't buy us much performance anyway. The obvious
drawback is that any code dealing with queries now has to handle two cases
(slow and fast).
In the future, we could optimize this further by combing fast and slow query
styles. For example, if you want to match with a substring *and* a regular
expression, we can do a first pass in SQLite and apply the regex predicate on
the results. Avoided for now because premature optimization, etc., etc.
Next step: implement flexattr matches as slow queries.
bs4 scraping routine has been made more generic,
relying less on specific markup tags.
Better algorithm to detect which url titles match
song titles: domain names are now removed from url
titles.
Use regex to decimate \n in fetched lyrics.
This also brought to light the fact that the distance calculations for tracks
was incorrect because there's no source field on TrackInfo objects yet. This
needs to be fixed.
