A few improvements to <script> functionality in Gon

Hi, your name is also Alex!

I was investigating an issue our application was having with Unicode Line separators, and noticed a regression in Gon. Gon used to handle \u2028 since it had backported the Rails escape_javascript helper, but this was removed somewhere down the line... https://github.com/gazay/gon/commit/ac33f7f01cb890dc97a4ae51ceda78230ba89fb9#L2R21

I've re-added this functionality.

Secondly, instead of escaping </script> tags with unicode, we can simply use the CDATA section so we can ensure data in Gon doesn't close our script tag for us by accident =) See here for more info: http://www.w3schools.com/xml/xml_cdata.asp

Anyway, these changes were kind of major, so I'm expecting some feedback.

Have a good one!