Also, I removed the @ from lookup_weaken since the Coq bug we
experienced before somehow disappeared.

Also, add algebra/gset to _CoqProject.

There was not really a need for the lattice type classes, so I removed
these.

These just make things more complicated, it would be more useful to
declare (efficient) decision procedures for each instance, so that
we can properly predict which instance we will get.

Similar files (gmap, listset, ...) were already in singular form and
matched the name of the set/map data type.

In particular, remove ectx_language.atomic, because it seems unused
expect for a smart constructor for language.atomic.

Also, remove some unused lemmas about agree.

* Values are considered as atomic expressions (this does not hurt, and
  this makes the proofs of atomicity simpler).

In order to improve flexibility, I have reverted the changes in commit
5cabd278 to counter, lock and spawn because an explicit namespace may be in
the way of modularity, for example, if the interfaces of these libraries will
expose namespaces through view shifts in the future.

Exposure of namespaces in the case of par is very unlikely, so to that end,
par remains to use an explicit namespace.

Both ndot and nclose involve encodings of countable types, and conversion
should thus never unfold these definitions.