migrate CI to GitHub Actions

use codecov.io to report on code coverage.
fix a few issues raised by golangci-lint

.github/workflows/linter.yaml

@@ -0,0 +1,18 @@
+on: [push, pull_request]
+name: linter
+
+jobs:
+  lint:
+    strategy:
+      matrix:
+        go-version: [1.x]
+        platform: [ubuntu-latest]
+    runs-on: ${{ matrix.platform }}
+
+    steps:
+    - uses: actions/checkout@v2
+
+    - name: golangci-lint
+      uses: golangci/golangci-lint-action@v2
+      with:
+        version: v1.41

.github/workflows/tests.yaml

@@ -0,0 +1,46 @@
+on: [push, pull_request]
+name: tests
+
+jobs:
+  test:
+    strategy:
+      matrix:
+        go-version: [1.x, 1.15.x]
+        platform: [ubuntu-latest]
+        include:
+          # only update test coverage stats with the most recent go version on linux
+          - go-version: 1.x
+            platform: ubuntu-latest
+            update-coverage: true
+    runs-on: ${{ matrix.platform }}
+
+    permissions:
+      # styfle/cancel-workflow-action needs to be able to cancel existing action workflows
+      actions: write
+
+    steps:
+    - name: Cancel previous
+      uses: styfle/cancel-workflow-action@89f242ee29e10c53a841bfe71cc0ce7b2f065abc #0.9.0
+      with:
+        access_token: ${{ github.token }}
+
+    - uses: actions/setup-go@v2
+      with:
+        go-version: ${{ matrix.go-version }}
+    - uses: actions/checkout@v2
+
+    - name: Cache go modules
+      uses: actions/cache@v2
+      with:
+        path: |
+          ~/.cache/go-build
+          ~/go/pkg/mod
+        key: ${{ runner.os }}-go-${{ hashFiles('**/go.sum') }}
+        restore-keys: ${{ runner.os }}-go-
+
+    - name: Run go test
+      run: go test -v -race -coverprofile coverage.txt -covermode atomic ./...
+
+    - name: Upload coverage to Codecov
+      if: ${{ matrix.update-coverage }}
+      uses: codecov/codecov-action@v2