This reverts merge request !309

This also applies to `(un)curry{3,4}`, `gmap_(un)curry`, and `h(un)curry`.

This fixes issue #76.

The code includes a horrible hack that should removed once support for Coq versions prior
to 8.13 is dropped.

This existed at least as far back as
iris/stdpp@361308c7, 8 years ago.

- Define set-like notation `{[+ x1; ..; xn ]}` for multisets in terms of the new
  singleton class and disjoint union `⊎`.
- Remove `SemiSet` instance for multisets.
- Prove lemmas regarding `∈` and `∉` for multisets since we no longer get the
  generic versions for sets.
- Provide `SetUnfoldElemOf` instances for multisets since we no longer get the
  generic versions for sets.
- Prove lemmas new regarding `∈` and `∉` for `∩`

Fixes #100, #98 and #87.

This MR is an alternative to !232.

Based on
https://github.com/coq/coq/issues/9058#issuecomment-496479506.

Fixes new Coq master warning deprecated-hint-without-locality.

These were very specific, there were no lemmas about them. They were used
back in the days for some specific things in my C semantics.

Fix in preparation for https://github.com/coq/coq/pull/13188

Tej Chajed authored 4 years ago and Robbert Krebbers committed 4 years ago

Set Default Goal Selector "!" makes it illegal to ever apply a tactic
with more than one goal (instead, must focus with bullets or braces).

Hugo Herbelin authored 4 years ago and Robbert Krebbers committed 4 years ago

This is a consequence of Coq PR #12950 which gives to import the
effect of reactivating the imported notations.

Use that in place of the old encoding:
iris/stdpp#70 (comment 52817)

Requires dropping support for Coq 8.7.

Fixes #67.