Add workflow to format code automatically

.github/workflows/autofmt.yml

@@ -0,0 +1,22 @@
+name: autofmt_push
+on: [push]
+jobs:
+  build:
+    runs-on: ubuntu-latest
+    steps:
+      - uses: actions/checkout@v2
+      - uses: actions-rs/toolchain@v1
+        with:
+            profile: minimal
+            toolchain: nightly
+            components: rustfmt
+      - run: cargo fmt -- --check
+      - name: If needed, commit cargo fmt changes
+        if: failure()
+        run: |
+          cargo fmt
+          git config --global user.name github-actions
+          git config --global user.email '${GITHUB_ACTOR}@users.noreply.github.com'
+          git remote set-url origin https://x-access-token:${{ secrets.GITHUB_TOKEN }}@github.com/$GITHUB_REPOSITORY
+          git commit -am "fixup! Format Rust code with rustfmt"
+          git push --force origin HEAD:$GITHUB_REF