Add unregister to IoC-Contrainer

Signed-off-by: Steven Klar <steven.klar@mayflower.de>

laravel/documentation/ioc.md

@@ -46,4 +46,13 @@ Now that we have SwiftMailer registered in the container, we can resolve it usin
 
 	$mailer = IoC::resolve('mailer');
 
-> **Note:** You may also [register controllers in the container](/docs/controllers#dependency-injection).
+> **Note:** You may also [register controllers in the container](/docs/controllers#dependency-injection).
+
+<a name="unregister"></a>
+## Unregister an existing instance
+
+For test purposes sometimes you need to unregister some container.
+
+#### Unregister example mail class:
+
+    IoC::unregister('mailer');