Added Curl Support and HttpClient Support on WinRT

This is a separate pull request to the other one.
Curl is now successfully compiled on WinRT as well as WP8
Please look to merge the other pull request first as I'm sure we will have many curl related issues on RT.
This also fixes an issue with using the windows 8 targeted 2012 project from vs2013 ;)

Otherwise this links perfectly and shouldn't break any other platform :)