add code coverage via cargo tarpaulin and coveralls

.github/workflows/coverage.yml

@@ -0,0 +1,22 @@
+name:                           coverage
+
+on:                             [ "push" , "pull_request" ]
+jobs:
+  test:
+    name:                       coverage
+    runs-on:                    ubuntu-latest
+    container:
+      image:                    xd009642/tarpaulin
+      options:                  --security-opt seccomp=unconfined
+    steps:
+      - name:                   Checkout repository
+        uses:                   actions/checkout@v2
+
+      - name:                   Generate code coverage
+        run: |
+          cargo tarpaulin --verbose --all-features --workspace --timeout 120 --out Lcov --output-dir coverage
+
+      - name:                   Upload to coveralls
+        uses: coverallsapp/github-action@master
+        with:
+          github-token: ${{ secrets.GITHUB_TOKEN }}