WIP: Add category support. (Added build dependency.)

.gitlab-ci.yml

 before_script:
-  - apt-get update -qq && apt-get install -y -qq python-virtualenv python3
+  - apt-get update -qq && apt-get install -y -qq python-virtualenv python3 python3-dev
   - virtualenv venv -p$(which python3)
   - . venv/bin/activate
   - pip install -r requirements.txt