ci: Add publishing workflow with GitHub Actions

* Test building a sdist and wheel on push events and pull request events
* List contents of sdist and wheel for visual checks / debugging
   - Note that check-manifest is currently incompatible with `prune **`
     strategy
* Publish sdists and wheels to TestPyPI through pushed tags triggered
  through push events
* Publish sdists and wheels to PyPI through published release events
  triggered through GitHub releases

.github/workflows/publish-package.yml

@@ -0,0 +1,64 @@
+name: publish distributions
+
+on:
+  push:
+    branches:
+    - main
+    tags:
+      - v*
+  pull_request:
+    branches:
+    - main
+  release:
+    types: [published]
+  workflow_dispatch:
+
+jobs:
+  build-and-publish:
+    name: Build and publish Python distro to (Test)PyPI
+    runs-on: ubuntu-latest
+
+    steps:
+
+    - name: Checkout
+      uses: actions/checkout@v2
+      with:
+        fetch-depth: 0
+
+    - name: Set up Python 3.9
+      uses: actions/setup-python@v2
+      with:
+        python-version: 3.9
+
+    - name: Install build and twine
+      run: |
+        python -m pip install --upgrade pip setuptools wheel
+        python -m pip install build twine
+        python -m pip list
+
+    - name: Build a sdist and a wheel
+      run: python -m build --outdir dist/ .
+
+    - name: Verify the distribution
+      run: twine check dist/*
+
+    - name: List contents of sdist
+      run: python -m tarfile --list dist/prettymaps-*.tar.gz
+
+    - name: List contents of wheel
+      run: python -m zipfile --list dist/prettymaps-*.whl
+
+    - name: Publish distribution 📦 to Test PyPI
+      # publish to TestPyPI on tag events
+      if: github.event_name == 'push' && startsWith(github.ref, 'refs/tags/v') && github.repository == 'marceloprates/prettymaps'
+      uses: pypa/gh-action-pypi-publish@v1.4.2
+      with:
+        password: ${{ secrets.test_pypi_password }}
+        repository_url: https://test.pypi.org/legacy/
+
+    - name: Publish distribution 📦 to PyPI
+      # publish to PyPI on releases
+      if: github.event_name == 'release' && github.event.action == 'published' && github.repository == 'marceloprates/prettymaps'
+      uses: pypa/gh-action-pypi-publish@v1.4.2
+      with:
+        password: ${{ secrets.pypi_password }}