Add AutoProxyServer

This adds automatic proxy server configuration on Windows.

When EnableAutoProxy is set (default), instances of the WebClient class will receive the appropriate proxy server for their BaseUrl.

Retrieves IE settings, including auto-detect and auto-config scripts and applies according to the specified BaseUrl.

Closes #69
I would move this inside of the actual function to remove the duplication here.

```VB.net
Public Function ...
#If Mac Then
    ' Windows only
#Else
    Dim ...
#End If
End Function