= New Features

* A detect_unnecessary_association_options plugin has been added,
  which warns or raises for unnecessary association options. For
  example, if you have an association such as:

    Album.many_to_one :artist, class: :Artist, key: :artist_id

  The plugin can inform you that the :class and :key options are
  unnecessary, since they are the same as Sequel's defaults for
  the options. That allows you to remove the unnecessary options:

    Album.many_to_one :artist

  The following unnecessary options are detected:

  * :class (all associations)
  * :key and :primary_key (associations without join tables)
  * :join_table, :left_key, :right_key, :left_primary_key,
    :right_primary_key (single join table associations)
  * :left_primary_key, :right_primary_key (*_through_many
    associations)

  To use the plugin, generally you would load it into the base model
  class before loading subclasses:

    Sequel::Model.plugin :detect_unnecessary_association_options

  After loading subclasses, you would call the 
  detect_unnecessary_association_options method on the subclasses.
  If you are using the subclasses plugin, this can be done via:

    Sequel::Model.descendants.each(&:detect_unnecessary_association_options)

  Detection also happens implicitly when finalizing associations,
  so the following will also work with the subclasses plugin:

    Sequel::Model.freeze_descendants

  By default, the plugin warns for unnecessary association options.
  To have it raise an error instead:

    Sequel::Model.plugin :detect_unnecessary_association_options, action: :raise
