This generalization is surprisingly easy in Iris 3.0, so I could not
resist not doing it :).

This makes stuff more uniform and also removes the need for the [inGFs]
type class. Instead, there is now a type class [subG Σ1 Σ2] which expresses
that a list of functors [Σ1] is contained in [Σ2].

In most cases it is a temporary whose name is useless and just
clutters the error message.

This commit reverts cdce49a7, which turns out to be no longer useful,
and which I thus no longer wish to maintain.

I do not know why we have to split the rewrite here, but it seems we do.

This is probably due to a bug in the rewrite of ssreflect 1.6 which has
been fixed in ssreflect master.

I cannot reproduce the error of the CI builder on my machine with the
same version of Coq (8.5pl2).

This better reflects the name of the bind rule.

I renamed an internal tactic that was previously called wp_bind into
wp_bind_core.

This fixes issue #25.

And make it Typeclasses Opaque to ensure that we indeed do not do
so using the proof mode.

Instead of having connectives pvs0 and pvs1 we now have one connective
pvs that is indexed by a Boolean.

Use it to prove that tests/barrier_client and tests/heap_lang are adequate.