using composer package format, decoupling bsr libraries and implementation

src/Exception/UsageException.php

@@ -0,0 +1,19 @@
+<?php
+
+namespace BSR\Lib\Exception;
+
+/**
+ * This exception should be raised by the WebService engine when
+ * there is an error preventing the correct calling of a method.
+ *
+ * @package BSR\Lib\Exception
+ */
+class UsageException extends WebException {
+    const NO_ARGS = 100;
+
+    const MISSING_METHOD = 101;
+    const BAD_METHOD = 102;
+
+    const TOO_FEW_ARGS = 103;
+    const TOO_MANY_ARGS = 104;
+}