0.16.0

• #237: allows bulk delete of model instances via the allow_delete_many
  keyword argument.
• #313, #389: APIManager.init_app now can be correctly used to
  initialize multiple Flask applications.
• #327, #391: allows ordering searches by fields on related instances.
• #353: allows search queries to specify group_by directives.
• #365: allows preprocessors to specify return values on get
  requests.
• #385: makes the include_methods keywords argument respect model properties.