Add GitHub action to build, test, and upload coverage

Based on `.travis.yaml`, which is not in use anymore.

.github/workflows/go.yml

@@ -0,0 +1,30 @@
+# https://docs.github.com/en/actions/automating-builds-and-tests/building-and-testing-go
+
+name: Go
+
+on:
+  push:
+    branches: [ "master" ]
+  pull_request:
+    branches: [ "master" ]
+
+jobs:
+
+  build:
+    runs-on: ubuntu-latest
+    steps:
+    - uses: actions/checkout@v3
+
+    - name: Set up Go
+      uses: actions/setup-go@v4
+      with:
+        go-version: '1.20'
+
+    - name: Build
+      run: go build -v ./...
+
+    - name: Test
+      run: sh ./test.sh
+
+    - name: Upload coverage data
+      run: bash <(curl -s https://codecov.io/bash)