* some cosmetics

* use backward Euler instead of BDF2

* preparing scaling with velocity (commented)

points...

* removed accessor for Dof (is already inherited from HyperbolicSolver)
* improved documentation
* cosmetics

* cosmetics

Hope it will help!

not test (in opt mode).

added a way to compute at each time step the mean flux
and the area of a section in the NS solver.
A first pre-process is done to get the faces that live
on the sought sections (search on points).
Then a special post-process is performed (it is called at each time step).

This function heavily depends on the mesh : OK for cylinders!