move global constants to class, make file structure PSR-0 compatible, add gitignore

Author: caseycs

.gitignore

@@ -0,0 +1 @@
+.idea

composer.json

@@ -16,6 +16,8 @@
         }
     ],
     "autoload": {
-        "classmap": ["sphinxapi.php"]
+        "psr-0": {
+            "SphinxApi": "src/"
+        }
     }
 }