Add github actions CI config

.github/workflows/ci.yml

@@ -0,0 +1,73 @@
+name: CI (tests, code style, phpstan)
+
+on: push
+
+jobs:
+  cs:
+    name: PHP CS Fixer
+    runs-on: ubuntu-latest
+
+    steps:
+      - name: Checkout code
+        uses: actions/checkout@v2
+
+      - name: Install PHP
+        uses: shivammathur/setup-php@v2
+        with:
+          php-version: '7.4'
+
+      - name: Check PHP Version
+        run: php -v
+
+      - name: Install dependencies
+        run: composer install --prefer-dist --no-progress --no-suggest
+
+      - name: Run PHP CS Fixer
+        run: composer cs
+
+  tests:
+    name: PHPUnit tests
+    runs-on: ubuntu-latest
+    strategy:
+      matrix:
+        php-versions: ['7.4', '8.0']
+
+    steps:
+      - name: Checkout code
+        uses: actions/checkout@v2
+
+      - name: Install PHP
+        uses: shivammathur/setup-php@v2
+        with:
+          php-version: ${{ matrix.php-versions }}
+
+      - name: Check PHP Version
+        run: php -v
+
+      - name: Install dependencies
+        run: composer install --prefer-dist --no-progress --no-suggest
+
+      - name: Run tests
+        run: composer test
+
+  stan:
+    name: PHPStan
+    runs-on: ubuntu-latest
+
+    steps:
+      - name: Checkout code
+        uses: actions/checkout@v2
+
+      - name: Install PHP
+        uses: shivammathur/setup-php@v2
+        with:
+          php-version: '7.4'
+
+      - name: Check PHP Version
+        run: php -v
+
+      - name: Install dependencies
+        run: composer install --prefer-dist --no-progress --no-suggest
+
+      - name: Run PHPStan
+        run: composer stan