Log Message:
Update py-beets to 1.5.0, PR pkg/56378.

This long overdue release of beets includes far too many exciting and useful
features than could ever be satisfactorily enumerated.
As a technical detail, it also introduces two new external libraries:
MediaFile and Confuse used to be part of beets but are now reusable
dependencies---packagers, please take note.
Finally, this is the last version of beets where we intend to support Python
2.x and 3.5; future releases will soon require Python 3.6.