Add caching and composer auth

.gitignore

@@ -1 +1,4 @@
 /.idea
+/.gitlab-ci.debug.yml
+/builds
+/cache

.gitlab-ci.yml

@@ -5,8 +5,14 @@ services:
 
 pages:
   stage: deploy
+  cache:
+    paths:
+    - composer
   script:
-  - docker run --rm -i -v `pwd`:/build composer/satis
+  - realpath composer || mkdir composer
+  - echo "$AUTH_JSON" > composer/auth.json
+  - docker run --rm -i -v `pwd`:/build -v `pwd`/composer:/composer composer/satis
+  - rm -f composer/auth.json # don't store auth
   artifacts:
     paths:
     - output