Safrs

* `jsonapi_attr` decorator
* granular permission checks (`SAFRSBase._s_check_perms`)
* included[] bug fix reported by Matt Leiter
* pip20 setup.py bug fix reported by polyatail

- Custom decorators
- setup.py download link
- Custom columns and relationships

51: render default column value in the swagger

- Remove debug print

- Bulk post (jsonapi bulk extension)
- More strict content type checking

- Limit allowed relationships, attributes, http methods
- Allow Model-less instances