Add linting GH action

Author: Seldaek

.github/workflows/lint.yml

@@ -0,0 +1,32 @@
+name: "PHP Lint"
+
+on:
+  - push
+  - pull_request
+
+jobs:
+  tests:
+    name: "Lint"
+
+    runs-on: ubuntu-latest
+
+    strategy:
+      matrix:
+        php-version:
+          - "5.3"
+          - "latest"
+
+    steps:
+      - name: "Checkout"
+        uses: "actions/checkout@v2"
+
+      - name: "Install PHP"
+        uses: "shivammathur/setup-php@v2"
+        with:
+          coverage: "none"
+          extensions: "intl"
+          ini-values: "memory_limit=-1, error_reporting=E_ALL, display_errors=On"
+          php-version: "${{ matrix.php-version }}"
+
+      - name: "Lint PHP files"
+        run: "find src/ -type f -name '*.php' -print0 | xargs -0 -L1 -P4 -- php -l -f"