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 think getting the proxy server should happen later in the process, ideally once you need it in `Get ProxyServer`. 

Maybe something like:

```VB.net
Public Property Get ProxyServer() As String
    If Me.EnableAutoProxy And Not pAutoProxyLoaded Then
        pProxyServer = WebHelpers.AutoProxyServer(Me.BaseUrl)
        pAutoProxyLoaded = True
    End If

    ProxyServer = pProxyServer
End Property

Public Property Let BaseUrl(Value As String)
    pBaseUrl = Value
    pAutoProxyLoaded = False
End Property
```