add gitlab ci configuration

.gitlab-ci.yml

+---
+
+image: stretch_python
+
+before_script:
+  - export LANG=en_US.UTF-8
+
+stages:
+  - test
+
+test:
+  stage: test
+  script:
+    - "python3 -m py_compile *.py"
+    - flake8 .