Return sticker recordings as multiple values

* contrib/sly-mrepl.el (sly-mrepl--copy-objects-to-repl): Add a bit of docstring.
(sly-stickers-copy-last-recording-to-repl): Clarify meaning of returned value.

* contrib/slynk-mrepl.lisp (globally-save-object): Fix docstring.
(copy-to-repl): Add a bit of doc.

* contrib/slynk-stickers.lisp (find-recording-or-lose): Return multiple values.