Still some way to go, but already workable.

* sly.el (sly-compilation-position): Factor out of sly-compile-string.
(sly-after-compile-functions): New variable.
(sly-before-compile-functions): Change semantics slightly.
(sly-compile-file): Call with current buffer.
(sly-compile-region): Pass hook to `sly-compile-string' so
`sly-after-compile-functions' can be called.

* slynk.asd (:slynk-stickers): Add system.

* contrib/sly-stickers.el (sly-stickers): Add slynk-dependencies.
(sly-stickers-mode-map): Use C-c C-s as a prefix map.
(sly-stickers--stickers, sly-stickers--sticker-keymap)
(sly-stickers--make-sticker, sly-stickers--sticker-id)
(sly-stickers--arm-sticker, sly-stickers--disarm-sticker)
(sly-stickers--populate-sticker)
(sly-stickers--bring-out-your-dead): New.
(sly-stickers-dwim): Use `sly-stickers--make-sticker'
(sly-stickers-fetch): New function.
(sly-stickers-commit-stickers): Redesign.

* contrib/sly-stickers.el (sly-stickers-mouse-hover-face): New face.