teach emacs to use wl-copy

wl-clipboard.el

  (setq wl-copy-process nil)
  (defun wl-copy (text)
    (setq wl-copy-process (make-process :name "wl-copy"
                                        :buffer nil
                                        :command '("wl-copy" "-f" "-n")
                                        :connection-type 'pipe))
    (process-send-string wl-copy-process text)
    (process-send-eof wl-copy-process))
  (defun wl-paste ()
    (if (and wl-copy-process (process-live-p wl-copy-process))
        nil ; should return nil if we're the current paste owner
        (shell-command-to-string "wl-paste -n | tr -d \r")))
  (setq interprogram-cut-function 'wl-copy)
  (setq interprogram-paste-function 'wl-paste)