Added in the ability to pass in a phantomjs configuration file.

[seanmwalker]

Hi,

We've run into some challenges running this tool against some of our sites, and found that setting headers and cookies for the phantomjs process was what we needed. Using the approach I've put in here will let any consumer of this module setup the request in a way that meets their needs. If there is anything I can do to help in getting either this change in, or one that will accomplish the same task, please let me know. Thanks!