Add Github Actions build.

.github/workflows/main.yml

@@ -0,0 +1,38 @@
+name: build
+
+on: [push]
+
+jobs:
+  build:
+    strategy:
+      matrix:
+        os: [ubuntu-latest, macOS-latest, windows-latest]
+        python-version: [3.7]
+    runs-on: ${{ matrix.os }}
+    env:
+      # TODO: remove this when github actions support "if" in expressions
+      PYTHON_VERSION: ${{ matrix.python-version }}
+      CODECOV_TOKEN: ${{ secrets.CODECOV_TOKEN }}
+
+    steps:
+    - uses: actions/checkout@master
+    - name: Set up Python ${{ matrix.python-version }}
+      uses: actions/setup-python@master
+      with:
+        python-version: ${{ matrix.python-version }}
+    - name: Update pip
+      run: |
+        python -m pip install --upgrade pip
+    - name: Lint with flake8
+      run: |
+        pip install flake8
+        # stop the build if there are Python syntax errors or undefined names
+        flake8 . --count --select=E9,F63,F7,F82 --show-source --statistics
+        # exit-zero treats all errors as warnings. The GitHub editor is 127 chars wide
+        flake8 . --count --exit-zero --max-complexity=10 --max-line-length=127 --statistics
+    - name: Test with tox
+      shell: bash
+      run: |
+        pip install tox
+        # remove the "." in the python version
+        tox -e "py${PYTHON_VERSION//.}"