#118: Set up complete CI/CD pipeline

Close #118 (closed).

.gitlab-ci.yml

 stages:
-  - format
-  - test
-  - build
+  - checks
+  - tests
   - release
   - publish_doc
 
 variables:
   DOCKER_IMAGE: "registry.duniter.org/docker/python3/poetry"
-  PYTHON_VERSION: "3.5"
+  PYTHON_VERSION: "3.8"
 
 image: $DOCKER_IMAGE/$PYTHON_VERSION:latest
 
-# SUB-TASKS
 .push_to_github:
   tags:
     - github
@@ -31,47 +29,81 @@ image: $DOCKER_IMAGE/$PYTHON_VERSION:latest
     # github push
     - bash -c "git push --force --mirror github 2>&1 | grep -v duniter-gitlab; echo $?"
 
+.code_changes:
+  only:
+    changes:
+      - duniterpy/**/*.py
+      - tests/**/*.py
+      - examples/*.py
+
 .changes:
   only:
     changes:
       - duniterpy/**/*.py
+      - tests/**/*.py
+      - examples/*.py
       - .gitlab-ci.yml
       - Makefile
-      - tests/**/*.py
       - pyproject.toml
 
-# TASKS
 format:
   extends:
-    - .changes
-  stage: format
-  image: $DOCKER_IMAGE/3.8:latest
+    - .code_changes
+  stage: checks
   script:
     - make check-format
 
-test:
+build:
   extends:
     - .changes
-  stage: test
+  stage: checks
   script:
-    - poetry install --no-dev
-    - make tests
+    - poetry build
 
-check:
+type:
   extends:
-    - .changes
-  stage: test
+    - .code_changes
+  stage: checks
   script:
-    - poetry install
     - make mypy
-    - make pylint
 
-build:
+lint:
   extends:
-    - .changes
-  stage: build
+    - .code_changes
+  stage: checks
   script:
-    - poetry build
+    - poetry install
+    - make pylint
+
+.tests:
+  extends: .changes
+  stage: tests
+  image: $DOCKER_IMAGE/$PYTHON_VERSION:latest
+  script:
+    - poetry install --no-dev
+    - make tests
+
+tests-3.5:
+  extends: .tests
+  tags: [poetry-56]
+  variables:
+    PYTHON_VERSION: "3.5"
+
+tests-3.6:
+  extends: .tests
+  tags: [poetry-56]
+  variables:
+    PYTHON_VERSION: "3.6"
+
+tests-3.7:
+  extends: .tests
+  tags: [poetry-78]
+  variables:
+    PYTHON_VERSION: "3.7"
+
+tests-3.8:
+  extends: .tests
+  tags: [poetry-78]
 
 release:
   extends:
@@ -99,7 +131,6 @@ pages:
     - tags
     - master
   script:
-    - poetry install
     - make docs
     - mv docs/_build/html public
     - ls public