Update testing: add docs + lint jobs; use pre-commit for linting (#426)

* Move docs and lint to their own [3.8] build job for more parallelism

* No codecov for docs or lint

* Move isort into pre-commit

* Add some handy linters to pre-commit

* Add rst-backticks linter and fix the errors

* Add pyupgrade and add upgrades

* Test docs and lint on GitHub Actions

* Xenial is default

.github/workflows/docs-lint.yml

@@ -0,0 +1,30 @@
+name: Docs and lint
+
+on: [push, pull_request]
+
+jobs:
+  build:
+    runs-on: ubuntu-latest
+    strategy:
+      matrix:
+        python-version: [3.8]
+        env:
+        - TOXENV: docs
+        - TOXENV: lint
+
+    steps:
+      - uses: actions/checkout@v1
+
+      - name: Set up Python ${{ matrix.python-version }}
+        uses: actions/setup-python@v1
+        with:
+          python-version: ${{ matrix.python-version }}
+
+      - name: Install dependencies
+        run: |
+          python -m pip install --upgrade pip
+          python -m pip install --upgrade tox
+
+      - name: Tox
+        run: tox
+        env: ${{ matrix.env }}