Based om iris/iris!467 (comment 53064)
by @Blaisorblade.

Improve some iIntros error messages

See merge request iris/iris!517

A failing iIntros for implications should prettify the identifier before
printing, and iIntros on something that isn't a wand or implication
should say what couldn't be introduced (to clarify that `iIntros "HP
HQ"` failed because of the HQ in particular, for example).

ghost-var lib: more lemmas for when you own the two halves

See merge request iris/iris!511

Fix direction of `auth_auth_validN`

See merge request iris/iris!515

For example, `auth_auth_valid`.

Fix error when destructing as multiple pats

See merge request iris/iris!512

`iDestruct H as "H1 H2"` produces an error that says the pattern should
contain exactly one proper introduction pattern. When multiple patterns
are provided, due to Ltac variable shadowing iDestructHypFindPat was
instead reporting only the first pattern in the error message (and even
that was printed as the parsed AST rather than the original string).

Report an error when iIntro fails to find a forall

See merge request iris/iris!510

The error handling for `iIntro (?)` and similar tactics didn't correctly
report failures when the goal couldn't be turned into a universal
quantifier. This is something missing from !482 due to no test
triggering the error.

use sep. conjunction instead of conjunction for allocation lemmas

See merge request !508

Fix compilation with Coq 8.10

See merge request !507

Fixes a bug from iris/iris!488

add a simple logic-level ghost_var library

See merge request iris/iris!488

This reverts commit 59280f68.
It was not actually needed.

wtf, sed?!??

Fix argument order in comment.

See merge request iris/iris!506

Isomorphism and validy restriction constructions for cameras.

See merge request iris/iris!504

rename `agree_op_{inv,invL}'` to `to_agree_op_{inv,invL}`

See merge request iris/iris!505