Fixed windows build behind proxy

Added casperjs to package.json so that npm could take care of downloading casper rather than doing it via the install.js script.
Removed install.js file since it wasn't needed. Modified casperjs script to simply look for casper in the correct location
Added npm install
Added npm preinstall
Added Node platform detection for casperjs to run on Windows
Merge pull request #62 from codice/master

Fixed windows build behind proxy