Reduce the number of directories distributed in the composer archive

composer.json

@@ -30,5 +30,8 @@
     "require-dev": {
         "phpunit/phpunit": "3.7.*",
         "phpunit/dbunit": "1.3.*"
+    },
+    "archive": {
+        "exclude": ["/demos", "/documentation", "/tests"]
     }
 }