Also fix a ton of bugs

* sly-stickers.el (sly-stickers--stickers-exactly-at): New function.
(sly-stickers--sticker-map): Get rid of
`sly-stickers-operate-on-sticker'
(sly-stickers--sticker): Error when trying to make a sticker for same coordinates
(sly-stickers--sticker-substickers): Check invariants.
(sly-stickers-clear-region-stickers): New interactive function.
(sly-stickers-clear-buffer-stickers): Use -region variant.
(sly-stickers-clear-defun-stickers): Use -region variant.
(sly-stickers-dwim): Improve and document.
(sly-stickers-operate-on-sticker): Remove.
(sly-stickers--delete): Remove from hashtable too.
(sly-stickers-commit-stickers): Temporary stickers buffer is hidden.
(sly-stickers--set-tooltip): New function.
(sly-stickers--sticker, sly-stickers--arm-sticker)
(sly-stickers--disarm-sticker, sly-stickers--populate-sticker):
Use it.

* slynk-stickers.lisp (check-stickers): Correctly iterate value
lists.