Network.Socket: Added CustomSockOpt data constructor for SocketOption
Merge pull request #123 from shockkolate/master

Network.Socket: Added CustomSockOpt data constructor for SocketOption
Bring latest GNU config in.
Remove pre-Windows XP wspiapi remains.
Make configure recognize mingw64.
Bump version number to 2.5.0.0

A new SocketOption constructor was added.
FFI wrapper for socket function.