Add GitHub Action for running tests.

.github/workflows/index.yml

@@ -0,0 +1,32 @@
+name: Build
+
+on:
+  push:
+  workflow_dispatch:
+
+jobs:
+  build:
+    runs-on: ubuntu-latest
+    strategy:
+      matrix:
+        python-version:
+          - 2.7
+          - 3.4
+          - 3.5
+          - 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 tox tox-gh-actions
+    - name: Run tests
+      run: |
+        tox