Automate push to pypi

Fixes #30

.github/workflows/pypi.yaml

@@ -0,0 +1,29 @@
+name: Push to PyPI
+
+on:
+  release:
+    types: [released, prereleased]
+
+jobs:
+  publish:
+    runs-on: ubuntu-latest
+
+    steps:
+    - uses: actions/checkout@v2
+    - name: Set up Python
+      uses: actions/setup-python@v2
+      with:
+        python-version: 3.7
+    - name: Install dependencies
+      run: |
+        python -m pip install --upgrade pip build
+    - name: Build the dataframe_expressions wheel
+      env:
+        dataframe_expressions_version: ${{ github.ref }}
+      run: |
+        python -m build --sdist --wheel
+    - name: Publish dataframe_expressions to PyPI
+      uses: pypa/[email protected]
+      with:
+        user: __token__
+        password: ${{ secrets.pypi_password_dataframe_expressions }}