Safrs

* HTTP Patch return 200
* Empty many-to-many relationships return `[]` instead of `null`
* Strict `include=` checking (return 400 in case of non-existing relationship)

* fix relationship sorting & filtering
* fix type json type coercion (by polyatail)
* http delete swagger response codes

* `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