Add whimrepl support for using vim-slime on Windows.

Hello,

I wrote a Leiningen plugin called [lein-whimrepl](https://github.com/malyn/lein-whimrepl) that wraps the standard Leiningen REPL in a Vim-targetable server on Win32 platforms.  You can then use Vim's remote protocol to send strings of text to the REPL.  This pull request adds support for that plugin to vim-slime.

Please let me know if you would like any changes/tweaks to this pull request.

Thanks!
Michael Alyn Miller