First attempt at GitHub CI.

Add .flake8 config file, we may use flake8 for linting.
We'd have to do a big code reformat for this to be done
for keepsies.

Add .github/workflows/drawdown.yml to run pytest and upload
to codecov.io.

.flake8

@@ -0,0 +1,7 @@
+[flake8]
+ignore =
+    # one blank line before docstring
+    D203,
+    E128, E126
+exclude = .git,__pycache__,voila
+max-complexity = 10

.github/workflows/drawdown.yml

@@ -0,0 +1,28 @@
+name: Drawdown Python application
+
+on: [push]
+
+jobs:
+  build:
+
+    runs-on: ubuntu-latest
+
+    steps:
+    - uses: actions/checkout@v1
+    - name: Set up Python 3.7
+      uses: actions/setup-python@v1
+      with:
+        python-version: 3.7
+    - name: Install dependencies
+      run: |
+        python -m pip install --upgrade pip
+        pip install -r requirements.txt
+    - name: Test with pytest
+      run: |
+        pip install pytest
+        pytest -v --cov=. --cov-report term --cov-report=xml --strict-markers
+    - name: Export to codecov.io
+      uses: codecov/[email protected]
+      with:
+        token: ${{secrets.CODECOV_TOKEN}}
+        file: ./coverage.xml