[x] Add documentation [x] Documentation: add relationships (secondary models) [ ] Use flask-marshmallow (make API HATEOAS-ready) [ ] Generalize use of API backend (So that it can use any ORM or OGM other than neomodel) [x] Fix validation_rules property to use datatypes of the model (bind them together somehow!) [x] Include unit-tests [x] Include serialization filtering on fields (return only specified fields) [x] Add unit-tests for put, patch and delete verbs