mediafile: update docs for MediaFile split

docs/dev/index.rst

@@ -4,8 +4,12 @@ For Developers
 This section contains information for developers. Read on if you're interested
 in hacking beets itself or creating plugins for it.
 
+See also the documentation for `MediaFile`_, the library used by beets to read
+and write metadata tags in media files.
+
+.. _MediaFile: http://mediafile.readthedocs.io/
+
 .. toctree::
 
     plugins
     api
-    media_file

docs/dev/media_file.rst

@@ -1,21 +0,0 @@
-.. _mediafile:
-
-MediaFile
----------
-
-.. currentmodule:: beets.mediafile
-
-.. autoclass:: MediaFile
-
-    .. automethod:: __init__
-    .. automethod:: fields
-    .. automethod:: readable_fields
-    .. automethod:: save
-    .. automethod:: update
-
-.. autoclass:: MediaField
-
-    .. automethod:: __init__
-
-.. autoclass:: StorageStyle
-    :members:

docs/dev/plugins.rst

@@ -370,17 +370,16 @@ template fields by adding a function accepting an ``Album`` argument to the
 Extend MediaFile
 ^^^^^^^^^^^^^^^^
 
-:ref:`MediaFile` is the file tag abstraction layer that beets uses to make
+`MediaFile`_ is the file tag abstraction layer that beets uses to make
 cross-format metadata manipulation simple. Plugins can add fields to MediaFile
 to extend the kinds of metadata that they can easily manage.
 
 The ``MediaFile`` class uses ``MediaField`` descriptors to provide
-access to file tags. Have a look at the ``beets.mediafile`` source code
-to learn how to use this descriptor class. If you have created a
-descriptor you can add it through your plugins ``add_media_field()``
-method.
+access to file tags. If you have created a descriptor you can add it through
+your plugins ``add_media_field()`` method.
 
 .. automethod:: beets.plugins.BeetsPlugin.add_media_field
+.. _MediaFile: http://mediafile.readthedocs.io/
 
 
 Here's an example plugin that provides a meaningless new field "foo"::