Clean up some exceptions, phpdoc

Lib/Exception/AuthenticationException.php

@@ -0,0 +1,15 @@
+<?php
+
+namespace BSR\Lib\Exception;
+
+/**
+ * This exception should be raised when an error
+ * related to the authentication mechanism arise.
+ *
+ * @package BSR\Lib\Exception
+ */
+class AuthenticationException extends WebException {
+    const USER_NOT_FOUND = 200;
+    const BAD_LOGIN = 201;
+    const AUTHENTICATION_FAILED = 202;
+}