add Go Actions

This adds Github Actions as CI.

.github/workflows/build.yml

@@ -0,0 +1,28 @@
+on: [push, pull_request]
+name: build
+jobs:
+  build:
+    strategy:
+      matrix:
+        go-version: [1.13.x, 1.14.x, 1.15.x]
+        os: [ubuntu-latest]
+    runs-on: ${{ matrix.os }}
+    steps:
+      - name: Install Go
+        uses: actions/setup-go@v2
+        with:
+          go-version: ${{ matrix.go-version }}
+      - name: Checkout code
+        uses: actions/checkout@v2
+      - name: Format Unix
+        if: runner.os == 'Linux'
+        run: test -z $(go fmt ./...)
+      - name: Test
+        run: go test -covermode atomic -coverprofile='profile.cov' ./...
+      - name: Send coverage
+        if: runner.os == 'Linux'
+        env:
+          COVERALLS_TOKEN: ${{ secrets.GITHUB_TOKEN }}
+        run: |
+          GO111MODULE=off go get github.com/mattn/goveralls
+          $(go env GOPATH)/bin/goveralls -coverprofile=profile.cov -service=github