RequestMarshaller complete

Request marshaller now returns an array of request objects that the runner can run. I have also added the relevant stubs that you can start filling in. Need to have a discussion around variable replacement in request urls and where should that go. :+1: 

Also, to see how this works, go to /newman/bin and run 

    ./newman -u https://www.getpostman.com/collections/fc3f0598daaa5271e4f7