Add an 'album_removed' event.

This works similarly to the existing 'item_removed' event but is called
with an `Album` object.

beets/library.py

@@ -878,6 +878,7 @@ class Item(LibModel):
             album = self.get_album()
             if album and not album.items():
                 album.remove(delete, False)
+                plugins.send('album_removed', album=album)
 
         # Send a 'item_removed' signal to plugins
         plugins.send('item_removed', item=self)

docs/changelog.rst

@@ -51,6 +51,8 @@ Other new things:
   yes`` in your configuration to enable.
 * :doc:`/plugins/fetchart`: A new option to change cover art format. Useful for
   DAPs that do not support some image formats.
+* New plugin event: ``album_removed``. Called when an album is removed from the
+  library (even when its file is not deleted from disk).
 
 For plugin developers:
 

docs/dev/plugins.rst

@@ -143,6 +143,9 @@ The events currently available are:
   command finishes adding an album to the library. Parameters: ``lib``,
   ``album``
 
+* `album_removed`: called with an ``Album`` object every time an album is
+  removed from the library (even when its file is not deleted from disk).
+
 * `item_copied`: called with an ``Item`` object whenever its file is copied.
   Parameters: ``item``, ``source`` path, ``destination`` path