Ormar

Fix issue 71

Fix issue 70

Fix for 68

* **Breaking:** QuerySet `bulk_update` method now raises `ModelPersistenceError` for unsaved models passed instead of `QueryDefinitionError`
* **Breaking:** Model initialization with unknown field name now raises `ModelError` instead of `KeyError`
* Added **Signals**, with pre-defined list signals and decorators: `post_delete`, `post_save`, `post_update`, `pre_delete`,
`pre_save`, `pre_update`
* Add `py.typed` and modify `setup.py` for mypy support
* Performance optimization
* Updated docs

* Performance optimization
* Fix for bug with `pydantic_only` fields being required
* Add `property_field` decorator that registers a function as a property that will
be included in `Model.dict()` and in `fastapi` response
* Update docs

Fix issue 60