Exposing Webternet functionality as natives

This patch exposes the HTTP logic of the Webternet extension as SourcePawn natives. 
See `plugins/include/webternet.inc` for a list of well commented natives. 

A sample plugin demonstrating the usage can be found [here](http://www.xup.to/dl,90855285/webtest.sp/).
I wasn't able to build it with MSCV 2010 'cause it can't be resolved so I hard coded it for the time developing with Visual Studio.