Flask-resty

**Feature:** Implement `|` operator on `Filtering` and `Related` (338)

- **Feature:** Allow disabling validation on cursor values (337)

- **Feature:** Extract `ApiError.from_validation_error` (333)

- **Refactor:** Move `Location` header logic to `make_item_response` (328)

- **Breaking:** Revamp upsert support (314)
- Add `GenericModelView.upsert` and remove `create_missing` in `GenericModelView.update`
- Unlike `GenericModelView.update` with `create_missing`, `GenericModelView.upsert` will call `ModelView.create_item` if there is no existing item, rather than calling `ModelView.update_item` on a stub item
- `GenericModelView.upsert` returns 201 if it creates a new item
- Rename `create_missing` option to `create_transient_stub` and rename `ModelView.create_missing_item` to `ModelView.create_stub_item`, to make it more clear what this functionality is supposed to do
- **Breaking:** Return 200 with item instead of 204 in `GenericModelView.update` (314)
- Remove the `return_content` option that previously enabled this behavior
- **Bugfix:** Make `objects` keyword-only in `ModelView.flush` (325)

- **Chore:** Fix wheel to not indicate Python 2 support (https://github.com/4Catalyzer/flask-resty/commit/53c69d6baab87ad1dd00535f04631aaa7443ba71)
- **Docs:** Fix documentation for response status code for `GenericModelView.destroy` (318)