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 know it's really annoying, but can you prefix all of the private function variables too? (e.g. `lpDest -> auto_lpDest`)

I'm not crazy about prefixing, but I've found it's helpful to reduce as many naming collisions as I can and limit the possibilities for messing with user's casing (upper vs. lower)