Add gitlab CI configuration.

.gitlab-ci.yml

+image: clarinpl/python:3.8
+
+stages:
+  - test
+  - deploy
+
+unittests:
+  stage: test
+  script:
+    - python setup.py test
+
+pypi_deploy:
+  before_script:
+   - pip install twine
+  only:
+   - master
+  stage: deploy
+  when: on_success
+  script:
+   - python setup.py sdist bdist_wheel
+   - python -m twine upload
+     --repository-url https://pypi.clarin-pl.eu/
+     -u $PIPY_USER
+     -p $PIPY_PASS
+     dist/COMBO*.whl