Fixes #176; Rewrite doc test

Merged from PR #178

* Update docs-check.yml

* Fix typo: "docs" -> "doc"

* Move "make html" to same shell as "cd" command

* Use sphinx-build command with -W flag

This makes it so that warnings are treated as errors (consistent with Read the Docs)

.github/workflows/docs-check.yml

@@ -5,9 +5,17 @@ jobs:
   docs:
     runs-on: ubuntu-latest
     steps:
-    - uses: actions/checkout@v1
-    - uses: ammaraskar/sphinx-action@master
+    - uses: actions/[email protected]
+    - name: Set up Python
+      uses: actions/setup-python@v2
       with:
-        docs-folder: "doc/"
-        pre-build-command: "pip3 install sphinx_rtd_theme"
-        build-command: "sphinx-build -T -E -W -b html . _build"
+          python-version: '3.x'
+    - name: Install Sphinx
+      run: |
+        python -m pip install --upgrade pip
+        pip install sphinx sphinx_rtd_theme
+    - name: Move to docs folder and build
+      run: |
+        cd doc
+        pwd
+        sphinx-build -T -E -W -b html . _build