trac #16622: Hypergraph is now an incidence structure
trac #16622: Changing the terminology
trac #16622: Broken doc
trac #16622: More doc fixes
trac #16622: HyperGraphGenerators --> HypergraphGenerators
Trac #16622: Deprecate Hypergraph in favor of IncidenceStructure

a "Hypergraph" class was introduced in #14712, but there also exists
`IncidenceStructure` in `sage/combinat/designs` as well as `set_system`
in `sage/matroids`.

We should really start to all work together on the same class, so for
now let's deprecate Hypergraph in favor of `IncidenceStructure`.

1) The only interesting thing that `Hypergraph` can do is plot a
hypergraph, and `IncidenceStructure` has no such feature.

2) Right now `set_system` claims to be only for internal use, so we
cannot use it right now as a replacement right now.

Nathann

URL: http://trac.sagemath.org/16622
Reported by: ncohen
Ticket author(s): Nathann Cohen
Reviewer(s): Dima Pasechnik