Fix documentation for ofe_funR

See merge request iris/iris!236

This comment wasn't updated after
866cad62.

Avoid conversion after only reducing goal.

See merge request iris/iris!235

If Ralf didn't know it, I guess it deserves a name. This is the first I got,
feel free to improve.

That's the documentation I'd have wanted to see, and viceversa the lack of this
rule implied (to me) that this wouldn't work.

Nicer soundness for our update modalities

See merge request iris/iris!230

Mentioned big_sepL2/sepM2 in the changelog.

See merge request iris/iris!232

The `2: { ... }` syntax is not yet supported there.

big_sepM2 and associated lemmas

See merge request iris/iris!228

Nicer soundness statements for the base_logic

See merge request iris/iris!229

This commit introduces the following soundness statements:

- Soundness of pure propositions `⌜ φ ⌝%I → φ`.
- Soundness of later `(▷ P)%I → P`.

The old soundness statement, `(▷^n ⌜ φ ⌝)%I → φ` is now a derived form.

Prophecy variables with lists

See merge request iris/iris!225