Turbasen

- feat: add `Liste`datatype

- feature: saving partial objects is now supported, using PATCH request
- fix: list requests returning no documents now works, returning empty list
- tests: various improvements
- development: docker image is now based on Alpine Linux

- dropped Python 2 support
- instances are now collections; document fields are stored in the collection, not as attributes
- removed `object_id` attribute abstraction, now stored transparently as field with key `_id`
- dropped concept of known datatype fields
- dropped concept of excludable common fields
- renamed method `lookup` to `list`
- removed `status=Offentlig` from default `list` parameters
- removed `tilbyder=DNT` from default `list` parameters
- renamed datatype `Omrade` to `Område`