ci: added CI to build documentation

.gitlab-ci.yml

+build-doc:
+    image: python:3.8
+    stage: build
+    script:
+        - pip install pdoc3
+        - pdoc --html src
+        - mkdir .public
+        - mv html/src/* .public/
+    artifacts:
+        paths:
+            - .public
+
+pages:
+  stage: deploy
+  script:
+    - mv .public public
+  artifacts:
+    paths:
+      - public
+  rules:
+    - if: $CI_COMMIT_BRANCH == $CI_DEFAULT_BRANCH