Add options to mail file

I have issue with Mbox class on my Linux system: I cannot open Mbox file because i receive Zend\Mail\Exception\RuntimeException with message: "Return-Path: <from@example.com> Delivered-To: to@example.com... does not match header format!".
This exception due to the fact my mbox file used a "\n" symbol as EOL.
This PR adds way to change EOL for Mbox files.