Gbd-mapping

- Documentation dependency update.

- Add coverage_gap of lack_of_vitamin_a_fortification

- Add a ``kind`` field to entities.
- Update covariates and coverage gaps mappings
- Remove HealthcareEntity
- Unpin click version

- Change setup.py
- Add coverage_gap of lack_of_immediate_assessment_and_stimulation exposure
- Add coverage_gap of lack_of_immediate_assessment_and_stimulation relative risk to (neonatal_preterm_birth_complications)

- Fix requirements.txt (add the click version)

- Add coverage_gap of lack_of_breastfeeding_promotion exposure
- Add coverage_gap of lack_of_lipid_lowering_therapy exposure