Check for Url and add Source action

2 steps here

First of all, this patch fixe a potentially bug with library and add a way to check the response of Uri to define if we display a link or an error.

In second time, this patch allow to use source as a keyword when the bot ins mention to get Uri for source code. You need to use class or path.

Example
 ```bash
Marvirc: source Hoa\Websocket
Marvirc: source Hoa\Websocket\Server
Marvirc: source Hoa/Websocket/Server.php
```
Use a long name, and initialize the `null`, not to an empty string.