rename sub_values -> sub_redexes_are_values

See merge request FP/iris-coq!79

Make atomic a type class.

See merge request FP/iris-coq!78

Thanks to Amin Timany for an initial version of the proof.

Make proofnode notation more robust in the context of import order

See merge request FP/iris-coq!75

This solves issue #100: the proof mode notation is sometimes not printed. As
Ralf discovered, the problem is that there are two overlapping notations:

```coq
Notation "P ⊢ Q" := (uPred_entails P Q).
```

And the "proof mode" notation:

```
Notation "Γ '--------------------------------------' □ Δ '--------------------------------------' ∗ Q" :=
  (of_envs (Envs Γ Δ) ⊢ Q%I).
```

These two notations overlap, so, when having a "proof mode" goal of the shape
`of_envs (Envs Γ Δ) ⊢ Q%I`, how do we know which notation is Coq going to pick
for pretty printing this goal? As we have seen, this choice depends on the
import order (since both notations appear in different files), and as such, Coq
sometimes (unintendedly) uses the first notation instead of the latter.

The idea of this commit is to wrap `of_envs (Envs Γ Δ) ⊢ Q%I` into a definition
so that there is no ambiguity for the pretty printer anymore.

This class, in combination with `TCForall`, turns out the useful in
LambdaRust to express that lists of expressions are values.

Rules for fancy updates and plain propositions.

Closes #105

See merge request FP/iris-coq!74

This commit is based on code by Amin Timany.

add a strong form of atomicity, for weak forms of weakest-pre

Closes #107

See merge request FP/iris-coq!77

This way, it can be used with `iApply`.

Notation for disjointness: replace ⊥ with ##, so that ⊥ can be used for bottom.

See merge request FP/iris-coq!73

This is to be used on top of stdpp's 4b5d254e.

Instead, as Ralf suggested, just comment the test out.