Add GitHub workflow for CPython

.github/workflows/test-python.yml

@@ -0,0 +1,29 @@
+name: elementpath
+
+on: [push, pull_request]
+
+jobs:
+  build:
+
+    runs-on: ubuntu-latest
+    strategy:
+      matrix:
+        python-version: [3.6, 3.7, 3.8, 3.9]
+
+    steps:
+      - uses: actions/checkout@v2
+      - name: Set up Python ${{ matrix.python-version }}
+        uses: actions/setup-python@v2
+        with:
+          python-version: ${{ matrix.python-version }}
+      - name: Install dependencies
+        run: |
+          python -m pip install --upgrade pip
+          pip install -r requirements-dev.txt
+          pip install flake8
+      - name: Lint with flake8
+        run: |
+          flake8 elementpath --ignore=F811 --max-line-length=100 --statistics
+      - name: Test with unittest
+        run: |
+          python tests/test_elementpath.py