I have reimplemented the tactic for introduction of ∀s/pures using type
classes, which directly made it much more modular.

The advantage is that we can directly use a Coq introduction pattern
`cpat` to perform actions to the pure assertion. Before, this had
to be done in several steps:

  iDestruct ... as "[Htmp ...]"; iDestruct "Htmp" as %cpat.

That is, one had to introduce a temporary name.

I expect this to be quite useful in various developments as many of
e.g. our invariants are written as:

  ∃ x1 .. x2, ⌜ pure stuff ⌝ ∗ spacial stuff.

Introduce a connective `ilocked` to stop `iNext` and `iFrame`.

See merge request FP/iris-coq!67

use primitive projections for our mixins

See merge request FP/iris-coq!69

Remove an unused argument for `newcounter_mono_spec`.

See merge request FP/iris-coq!70

update stdpp

See merge request FP/iris-coq!68