feat: switch to GitHub Actions (#72)

* feat: switch to GitHub Actions

* feat: add docker compose cache

* docs: add GH actions badge

.github/workflows/ci.yml

@@ -0,0 +1,33 @@
+name: CI
+
+on:
+    push:
+    pull_request:
+
+jobs:
+    build:
+        name: Docker build
+        runs-on: ubuntu-latest
+        steps:
+            - name: Checkout
+              uses: actions/checkout@v2
+            - name: Pull images
+              run: docker-compose pull
+            - uses: satackey/action-docker-layer-caching@v0.0.8
+              continue-on-error: true
+            - name: Start services
+              run: docker-compose up --build -d
+            - name: Wait for services
+              run: |
+                  while status="$(docker inspect --format="{{if .Config.Healthcheck}}{{print .State.Health.Status}}{{end}}" "$(docker-compose ps -q php)")"; do
+                    case $status in
+                      starting) sleep 1;;
+                      healthy) exit 0;;
+                      unhealthy) exit 1;;
+                    esac
+                  done
+                  exit 1
+            - name: Check HTTP reachability
+              run: curl http://localhost
+            - name: Check HTTPS reachability
+              run: curl -k https://localhost