Enable GitHub Actions runners to run tests (hardbyte#827)

GitHub announced Actions at GitHub Universe in 2018, however this was
somewhat limited, and support for running CI/CD pipelines was only
released in August 2019. This was in beta for a long time, and finally
has been rolled out to the general public.

This adds a minimal GitHub Actions workflow that runs all the current
tests on a build matrix consisting of {Ubuntu,macOS,Windows} and Python
3.{6,7,8}. This also seems to run much faster than the current Travis CI
pipelines, and actually lets us cover multiple versions on macOS without
a series of hacks.

Unfortunately, the kernel that GitHub Actions uses (5.0.0-1035-azure)
doesn't include the vcan kernel module, so we still need Travis CI to
run SocketCAN tests.

Author: karlding

.github/workflows/build.yml

@@ -0,0 +1,24 @@
+name: Tests
+
+on: [push, pull_request]
+
+jobs:
+  build:
+    runs-on: ubuntu-latest
+    strategy:
+      matrix:
+        os: [ubuntu-latest, macos-latest, windows-latest]
+        python-version: [3.6, 3.7, 3.8]
+    steps:
+    - uses: actions/checkout@v2
+    - name: Set up Python ${{ matrix.python-version }}
+      uses: actions/setup-python@v1
+      with:
+        python-version: ${{ matrix.python-version }}
+    - name: Install dependencies
+      run: |
+        python -m pip install --upgrade pip
+        pip install .[test]
+    - name: Test with pytest
+      run: |
+        pytest