Add automated continuous benchmarking

.github/workflows/bench.yml

@@ -0,0 +1,62 @@
+on:
+  push:
+    branches:
+      - main
+  pull_request:
+
+name: Benchmark
+
+jobs:
+  benchmark:
+    name: Benchmark
+    runs-on: ubuntu-latest
+    steps:
+      - uses: actions/checkout@v2
+
+      - uses: actions-rs/toolchain@v1
+        with:
+          profile: minimal
+          toolchain: stable
+          override: true
+
+      - uses: actions/cache@v2
+        with:
+          path: |
+            ~/.cargo/registry
+            ~/.cargo/git
+            target
+          key: cargo-${{ runner.os }}-bench-${{ hashFiles('**/Cargo.toml') }}
+        continue-on-error: true
+
+      - name: Run benchmarks
+        run: |
+          for bench in call dict gil list pyclass pyobject set tuple; do
+            cargo bench --features hashbrown --bench "bench_$bench" -- --output-format bencher | tee -a output.txt
+          done
+
+      # Download previous benchmark result from cache (if exists)
+      - name: Download previous benchmark data
+        uses: actions/cache@v1
+        with:
+          path: ./cache
+          key: ${{ runner.os }}-benchmark
+
+      # Run `github-action-benchmark` action
+      - name: Store benchmark result
+        uses: rhysd/github-action-benchmark@v1
+        with:
+          name: pyo3-bench
+          # What benchmark tool the output.txt came from
+          tool: 'cargo'
+          # Where the output from the benchmark tool is stored
+          output-file-path: output.txt
+          # # Where the previous data file is stored
+          # external-data-json-path: ./cache/benchmark-data.json
+          # Workflow will fail when an alert happens
+          fail-on-alert: true
+          # GitHub API token to make a commit comment
+          github-token: ${{ secrets.GITHUB_TOKEN }}
+          # Enable alert commit comment
+          comment-on-alert: true
+          alert-comment-cc-users: '@PyO3/pyo3'
+          auto-push: ${{ github.event_name != 'pull_request' }}