Initialize winsock with version 2.2

[trueqbit]

asio::detail::winsock_init initalizes winsock with v2.0.

Not sure whether this makes any difference for asio and the world in general, I just think it's a good idea to default to the latest version.

• v2.0 was only an internal draft version.
• v2.1 was the first public winsock 2 specification.
• Nobody needs 16-bit OS support these days anymore?
• v2.2 itself is ages old, and supported back to Windows 95 OSR2.