Integrating PhantomJS

I started integrating PhantomJS into the crawler then stopped myself because I didn't want to hack the code up or do it in a way that you may have not preferred. There are a number of ways you can go about doing this, the preferable way in my opinion would most likely be as a separate function; but since I am not as familiar with the code as you, the author, it's probably best that you go about that part of the integration.

If you have any questions let me know. Running a simple exec() with the command below and waiting on the callback for stdin or stderr should suffice.

**An example of how to run this with PhantomJS:**
phantomjs lib/phantom.js --useragent="Test Agent" --timeout=10000 --url=http://angularjs.org