Implemented short code generation based on a provided long URL

src/Exception/InvalidUrlException.php

@@ -0,0 +1,11 @@
+<?php
+namespace Acelaya\UrlShortener\Exception;
+
+class InvalidUrlException extends RuntimeException
+{
+    public static function fromUrl($url, \Exception $previous = null)
+    {
+        $code = isset($previous) ? $previous->getCode() : -1;
+        return new static(sprintf('Provided URL "%s" is not an exisitng and valid URL', $url), $code, $previous);
+    }
+}