Vendor the stdlib expect for Windows sockets

`expect.rb` is part of the `pty` extension to the Ruby stdlib since it
uses `select` and is meant for use with things like pipes or terminals
and Windows does not allow for selecting on those sorts of handles.
Since we only use it for sockets, we can pull it in straight to allow
for use on Windows without building the whole `pty` extension.

LICENSE

@@ -71,6 +71,10 @@ Files: lib/anemone.rb lib/anemone/*
 Copyright: 2009 Vertive, Inc.
 License: MIT
 
+Files: lib/expect.rb
+Copyright: 2017 Yukihiro Matsumoto
+License: Ruby
+
 Files: lib/msf/core/modules/external/python/async_timeout/*
 Copyright: 2016-2017 Andrew Svetlov
 License: Apache 2.0