[Matlab] Add basic nix.MultiTag documentation

- documentation for the MultiTag entity.
- rename addPositions to setPositions since it is more a setter than adding data.
- update addPositions tests.
- rename addFeature to createFeature since it actually creates a feature.
- update addFeature tests.
- rename removeFeature to deleteFeature since it actually deletes a feature.
- update removeFeature tests.

Author: mpsonntag