Changed autoload to "classmap"

S3.php bundles multiple classes, so "classmap" fits better

Author: zyberspace

composer.json

@@ -13,6 +13,6 @@
         "php": ">=5.2.0"
     },
     "autoload": {
-        "psr-0": { "S3": "" }
+        "classmap": ["S3.php"]
     }
 }