Merge pull request #9 from clue/psr4

Use PSR-4 layout for src/

Author: clue

composer.json

@@ -5,7 +5,7 @@
     "keywords": ["udp", "datagram", "dgram", "socket", "client", "server", "react", "async"],
     "license": "MIT",
     "autoload": {
-        "psr-0": {"Datagram": ""}
+        "psr-4": {"Datagram\\": "src"}
     },
     "require": {
         "react/event-loop": ">=0.2, <0.4",