style tweaks & doc expansion (#98)
max_rec (#98): more lenient defaults

These defaults more closely reflect the current behavior of beets, which I
think is desirable.
max_rec (#98): fix bug w/ multiple track triggers

If both "tracklength" and "tracknumber" triggers occur for a certain album,
then the *lowest* recommendation max should be used. (With the `break`s in
there, it would just be the first trigger found.)