added PSR-4 autoload

Author: adriangibbons

composer.json

@@ -7,5 +7,10 @@
     "require-dev": {
         "phpunit/phpunit": "4.8.*",
         "squizlabs/php_codesniffer": "2.*"
+    },
+    "autoload": {
+        "psr-4": {
+            "adriangibbons\\": "src/"
+        }
     }
-}
+}