Add coveralls integration (#645)

Author: jackfirth

.github/workflows/main.yml

@@ -11,5 +11,9 @@ jobs:
       - uses: Bogdanp/[email protected]
         with:
           version: stable
+      - run: raco pkg install --batch --auto cover cover-coveralls
       - run: raco pkg install --batch --auto --link --name resyntax
       - run: raco test --package resyntax
+      - run: raco cover --format coveralls --package resyntax
+        env:
+          COVERALLS_REPO_TOKEN: ${{ secrets.COVERALLS_REPO_TOKEN }}