Added the exception class and updated composer file

Author: Repox

composer.json

@@ -1,5 +1,7 @@
 {
     "name": "repox/swipbox",
+    "version": "1.0.1-dev",
+    "type": "library",    
     "description": "Client Library for Swipbox API integration",
     "license": "MIT",
     "authors": [

src/Swipbox/Exception.php

@@ -0,0 +1,14 @@
+<?php namespace Swipbox;
+
+class Exception extends \Exception
+{
+	public function __construct($message, $code = 0, Exception $previous = null) 
+	{
+		parent::__construct($message, $code, $previous);
+	}
+
+	public function __toString()
+	{
+		return __CLASS__ . ": [{$this->code}]: {$this->message}\n";
+	}	
+}