release 0.15

[jeremyandrews]

0.15.0 November 2, 2021

• #372 de-deduplicate documentation, favoring The Goose Book
• #373 API change: introduce GooseRequest and GooseRequestBuilder for more flexibility when making requests
  o remove GooseUser::post_named, GooseUser::head_named, GooseUser::delete_named, GooseUser::goose_get, GooseUser::goose_put, GooseUser::goose_head, GooseUser::goose_put, GooseUser::goose_patch, GooseUser::goose_delete, and GooseUser::goose_send
  o adds or modifies helpers GooseUser::get, GooseUser::get_named, GooseUser::post, GooseUser::post_form, GooseUser::post_json, GooseUser::head, and GooseUser::delete
  o replaces GooseUser::goose_send with GooseUser::request which accepts a GooseRequest object
  o fixes [errors updated to success with set_success() show up in error summary #370] (see GooseRequestBuilder::expect_status_code)