Remove coercion `iMsg_car` and `Proper` instances to avoid one accidentally breaking the `iMsg` abstraction.

- Protocols are no longer contractive in the message
- New type `iMsg` for messages to avoid telescopes in protocols
- Better rules for subprotocols that do not involve telescopes, but allow introduction
  and elimination of quantifiers and the payload
- Better notations for protocols
- Notation ⊑ for subprotocols
- Make ⊑ except-0 so one can strip laters when proving a ⊑
- Restore recursive domain equation to push later inwards to support protocols
  that are not contractive in the mssage.
- Proofmode support for easy manipulation of ⊑

Kinded subtyping, better file structure, more setoid stuff, reorganize imports.

By moving the later further to the outside, we can kill many occurences
of `Next`, and get rid of laters/except_0s at awkward positions. Also we
can have a sensible eliminator `proto_elim`.

Moved Iris specific stuff into a utility file.

TODO: fix in-place merge function.

- Allow for binders in protocols.
- Model protocols in CPS style using the COFE solver.
- Change the channel methods so they do not mention sides.
- Lots of refactoring.
- Generalize the `list_sort` example.
- Move stuff to stdpp/Iris.

- Put code and proofs of examples in a single file.
- Rename encode/decode to avoid conflicts with encode/decode (of the countable class) in stdpp.
- Remove useless imports.

commit 32f5885b5083c6052251a266b0ec4b6f0cd01bcc
Author: Jonas Kastberg Hinrichsen <jkas@itu.dk>
Date:   Tue Jun 11 11:54:32 2019 +0200

    Full bump

commit 3fdf913129ee6c1081e947de48e71ca6411f33da
Author: Robbert Krebbers <mail@robbertkrebbers.nl>
Date:   Tue Jun 11 11:31:22 2019 +0200

    More cleanup.

commit 46be8c0184d5a9e7de42022e389e23df99f73f6d
Author: Robbert Krebbers <mail@robbertkrebbers.nl>
Date:   Mon Jun 10 22:50:02 2019 +0200

    Some cleanup.

commit 2dc17e2cafc0b33e5ef0d2a6f6862b0938f68b18
Author: Jonas Kastberg Hinrichsen <jkas@itu.dk>
Date:   Mon Jun 10 16:33:46 2019 +0200

    WIP

commit 9427aa2ddd4fecb49b8e1c02eccc954fdb8af554
Author: Jonas Kastberg Hinrichsen <jkas@itu.dk>
Date:   Mon Jun 10 15:02:21 2019 +0200

    iRewrite Bug inspection

commit 40393f8800ab1a587f49f9ad479f5dc94b2bf2bc
Author: Jonas Kastberg Hinrichsen <jkas@itu.dk>
Date:   Mon Jun 10 14:56:08 2019 +0200

    Bumped Iris

commit 660218ca36e148b7270fd0044a2401fa553373d1
Author: Robbert Krebbers <mail@robbertkrebbers.nl>
Date:   Mon Jun 3 11:31:11 2019 +0200

    Add type.

commit 54214779390c19b1f9c8b293ac26f36efda95f4d
Author: Robbert Krebbers <mail@robbertkrebbers.nl>
Date:   Fri May 31 16:24:05 2019 +0200

    Coinductive version of stype.

commit b0fe9afb
Author: Robbert Krebbers <mail@robbertkrebbers.nl>
Date:   Fri May 31 13:19:13 2019 +0200

    Bump Iris.