Add Observer. Remove functions from python side and add as observer of Problem. Add loads directions as functions. Minor changes.

Add formulation classes to build set of equations, and remove build methods from Element (flow only).
Draft methods to compute freestream velocity.
Rework data structure of boundary.
Add const.
Improve test cases.

Refactor normal computation to remove duplicated code.

Limit pressure coef gradient for vacuum conditions. Raise tolerances to account for diff in mesh on diff machine. Rename variable to avoid keyword

New validated adjoint solver with gradients wrt to mesh and agnle of attack. Add mesh gradients computation in Element. Split run method in MshDeform. Minor changes.

Add automatic pin of a DOF if no Dirichlet BC is provided. Remove explicit Dirichlet, except in cylinder tests cases. Cleaning.

remove filter in VVI. Allow process to continue if Newton not fully converged. Improve tangent matrix computation. Clean

Squashed commit of the following:

commit c6c791de
Author: AmauryBilocq <amaury.bilocq@gmail.com>
Date:   Fri Nov 6 12:03:29 2020 +0100

    Quasi-simultaneous coupler for VII with test cases

commit 0cbee7e4
Merge: fd99999c ca62dcef
Author: AmauryBilocq <amaury.bilocq@gmail.com>
Date:   Sun Apr 26 14:58:26 2020 +0200

    V1.0 Viscous Inviscid interaction with direct solver

commit fd99999c
Author: AmauryBilocq <amaury.bilocq@gmail.com>
Date:   Sun Apr 26 14:47:01 2020 +0200

    V1.0 Viscous Inviscid interaction with direct solver

commit ca62dcef
Author: AmauryBilocq <amaury.bilocq@gmail.com>
Date:   Wed Oct 30 18:41:17 2019 +0100

    Trial to find the stagnation point

Refactor density computation. Limit Cp so that loads are always outputed even if solution is not locally converged.

Add interface for linear sovlers. Add macros definition at global level. Adapt modules to test the different linear solvers.