ci: set up CI with Github Actions

Note that because of a bug fix in Python 3.8, the position of
`noqa: F811` for @overload has to be changed (see also
https://gitlab.com/pycqa/flake8/issues/583). So, if we want to pass
flake8 both with Python 3.7 and 3.8, we need to put `noqa: F811` for two
lines per @overload. This situation will be resolved by a new release of
pyflakes with improving @overload detection PyCQA/pyflakes#435.

.github/workflows/ci.yml

@@ -0,0 +1,36 @@
+name: CI
+
+on: [push, pull_request]
+
+jobs:
+  lint:
+    strategy:
+      matrix:
+        python: [3.7, 3.8]
+    runs-on: ubuntu-latest
+    steps:
+      - uses: actions/checkout@v2
+      - uses: actions/setup-python@v1
+        with:
+          python-version: ${{ matrix.python }}
+      - name: Set PY
+        run: echo "::set-env name=PY::$(python --version --version | sha256sum | cut -d' ' -f1)"
+      - uses: actions/cache@v1
+        with:
+          path: ~/.cache/pre-commit
+          key: pre-commit|${{ env.PY }}|${{ hashFiles('.pre-commit-config.yaml') }}
+      - run: pip install gitlint
+      - run: gitlint
+      - uses: pre-commit/[email protected]
+  test:
+    strategy:
+      matrix:
+        os: [ubuntu-16.04, ubuntu-18.04]
+        python: [2.7, 3.5, 3.6, 3.7, 3.8]
+    runs-on: ${{ matrix.os }}
+    steps:
+      - uses: actions/checkout@v2
+      - uses: actions/setup-python@v1
+        with:
+          python-version: ${{ matrix.python }}
+      - run: python formset.py

formset.py

@@ -142,7 +142,7 @@ def round_human_readable(x, up, tostring):  # noqa: D103
 
 
 @overload  # noqa: F811
-def round_human_readable(x, up, tostring):  # noqa: D103
+def round_human_readable(x, up, tostring):  # noqa: D103, F811
     # type: (int, bool, Literal[False]) -> int
     pass