Handler for remote Syslogd logging

Hi!

First off, thank you all so much for a wonderful logging framework, I have been using it for quite a while, both on hobby projects and at work.

This pull request implements remote Syslogd logging. The idea is that you have a central Syslogd server, which all your application servers can log to. This was implemented at my work, because we host our site on EC2's with autoscaling. Thus, if we had a webnode which was terminated, we had no way of getting a hold of the logfiles.

Example usage:
```php
$logger = new \Monolog\Logger();
$handler = new SyslogUdpHandler("local5", "127.0.0.1");
$handler->setFormatter(new \Monolog\Formatter\LineFormatter());
$logger->pushHandler($handler);
$logger->warn("Hello from abroard!");
````

If you have suggestions for improvements I'd be happy to implement them :)