Add linting (pylint / mypy)

Signed-off-by: Maxime “pep” Buquet <pep@bouah.net>

.gitlab-ci.yml

+stages:
+- lint
+
+.python-3.7:
+  image: python:3.7
+
+.python-3.8:
+  image: python:3.8
+
+.pylint:
+  stage: lint
+  script:
+    - apt update && apt install -y libidn11-dev build-essential cmake
+    - pip3 install pylint pyasn1-modules cffi --upgrade
+    - pip3 install -e git+https://lab.louiz.org/poezio/slixmpp.git#egg=slixmpp
+    - pip3 install -e git+https://lab.louiz.org/poezio/slixmpp-omemo.git#egg=slixmpp-omemo
+    - pip3 install -e git+https://lab.louiz.org/poezio/poezio.git#egg=poezio
+    - python3 setup.py install
+    - pylint -E poezio_omemo
+
+.mypy:
+  stage: lint
+  script:
+    - pip3 install mypy
+    - mypyc --ignore-missing-imports ./poezio_omemo
+
+lint-3.7-pylint:
+  extends:
+    - .python-3.7
+    - .pylint
+
+lint-3.8-pylint:
+  extends:
+    - .python-3.8
+    - .pylint
+
+lint-3.7-mypy:
+  extends:
+    - .python-3.7
+    - .mypy
+
+lint-3.8-mypy:
+  extends:
+    - .python-3.8
+    - .mypy