Run CI on GitHub Actions, not Travis

* Run CI on GitHub Actions, not Travis - refs #940
* Update documentation refs to Travis
* Release action now runs parallel tests, then pushes to PyPI, then Docker Hub

.github/workflows/publish.yml

@@ -0,0 +1,72 @@
+name: Publish Python Package
+
+on:
+  release:
+    types: [created]
+
+jobs:
+  test:
+    runs-on: ubuntu-latest
+    strategy:
+      matrix:
+        python-version: [3.6, 3.7, 3.8]
+    steps:
+    - uses: actions/checkout@v2
+    - name: Set up Python ${{ matrix.python-version }}
+      uses: actions/setup-python@v2
+      with:
+        python-version: ${{ matrix.python-version }}
+    - uses: actions/cache@v2
+      name: Configure pip caching
+      with:
+        path: ~/.cache/pip
+        key: ${{ runner.os }}-pip-${{ hashFiles('**/setup.py') }}
+        restore-keys: |
+          ${{ runner.os }}-pip-
+    - name: Install dependencies
+      run: |
+        pip install -e '.[test]'
+    - name: Run tests
+      run: |
+        pytest
+  deploy:
+    runs-on: ubuntu-latest
+    needs: [test]
+    steps:
+    - uses: actions/checkout@v2
+    - name: Set up Python
+      uses: actions/setup-python@v2
+      with:
+        python-version: '3.8'
+    - uses: actions/cache@v2
+      name: Configure pip caching
+      with:
+        path: ~/.cache/pip
+        key: ${{ runner.os }}-publish-pip-${{ hashFiles('**/setup.py') }}
+        restore-keys: |
+          ${{ runner.os }}-publish-pip-
+    - name: Install dependencies
+      run: |
+        pip install setuptools wheel twine
+    - name: Publish
+      env:
+        TWINE_USERNAME: __token__
+        TWINE_PASSWORD: ${{ secrets.PYPI_TOKEN }}
+      run: |
+        python setup.py sdist bdist_wheel
+        twine upload dist/*
+  deploy_docker:
+    runs-on: ubuntu-latest
+    needs: [deploy]
+    steps:
+    - uses: actions/checkout@v2
+    - name: Build and push to Docker Hub
+      env:
+        DOCKER_USER: ${{ secrets.DOCKER_USER }}
+        DOCKER_PASS: ${{ secrets.DOCKER_PASS }}
+      run: |-
+         docker login -u $DOCKER_USER -p $DOCKER_PASS 
+         export REPO=datasetteproject/datasette 
+         docker build -f Dockerfile -t $REPO::${GITHUB_REF#refs/tags/} . 
+         docker tag $REPO::${GITHUB_REF#refs/tags/} $REPO:latest
+         docker push $REPO