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/).
The binary name define in the Resources > Preprocessor Definitions in the project is probably missing quotes if this is occurring. It should be something like:

`BINARY_NAME="\"$(TargetFileName)\""`