Basic Rust testing + merge commit detection with Github Actions

.github/workflows/enarx-standard.yml

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+name: Enarx Standard Tests
+# Automated testing common to all Enarx repositories.
+
+on: [push, pull_request]
+
+jobs:
+  commits:
+    runs-on: ubuntu-latest
+    steps:
+    - uses: actions/checkout@master
+      with:
+        ref: ${{ github.head_ref }}
+    # Ensure pull requests do not contain merge commits.
+    - name: No merge commits
+      # Merge commits have two parent commits. This command iterates through
+      # all commits added by the PR (everything since the base ref) and fails
+      # if it finds multiple parents. If all commits only have one, it exits 
+      # successfully.
+      run: git rev-list origin/${{ github.base_ref }}.. | xargs -n1 -I{} sh -c '! git rev-parse {}^2'

.github/workflows/rust.yml

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+name: Enarx Rust Tests
+# Automated testing specific to Enarx's Rust repositories.
+
+on: [pull_request]
+
+jobs:
+  # Ensure all code is properly formatted with `rustfmt`.
+  rust-formatting:
+    runs-on: ubuntu-latest
+    steps:
+    - uses: actions/checkout@v1
+    - name: rustfmt
+      run: cargo fmt -- --check
+
+  # Build and test the crate.
+  rust-build-test:
+    runs-on: ubuntu-latest
+    steps:
+    - uses: actions/checkout@v1
+    # Ensure the project builds correctly.
+    - name: Build
+      run: cargo build --verbose
+    # Run any specified Rust tests.
+    - name: Run tests
+      run: cargo test --verbose