Callback for Mandril Handler

The following code can be used to silence the curl response. It also allows you to pass in a call back function which can then be used to process the response from mandrill. 
We were using this project in a website and upon sending an email to mandrill, the response was being echoed out on our site. 
This shouldn't be pushed to the Monolog repository since it is dependent on your IDE. You can add it to your local `.git/info/exclude` file to not having it displayed as a new file.