Merge pull request json-schema-org#45 from yuloh/readd-json-guard

Re-add PHP validator JSON Guard

Author: Relequestual

implementations.html

@@ -62,6 +62,7 @@ <h2>Validators</h2>
 		<li><a id="link-impl-php-json-schema" href="https://github.com/hasbridge/php-json-schema">php-json-schema</a> (MIT)</li>
 		<li><a id="link-impl-json-schema" href="https://github.com/justinrainbow/json-schema">json-schema</a> (Berkeley)</li>
 		<li><a id="link-impl-jval" href="https://github.com/stefk/jval">JVal</a> - <em>supports version 4</em>  (MIT)</li>
+		<li><a id="link-impl-json-guard" href="https://github.com/thephpleague/json-guard">JSON Guard</a> - <em>supports version 4</em> (MIT)</li>
 	</ul>
 	</li>
 	<li>.NET