Fluid2d is replaced with Fluids2d

[pvthinker]

Fluid2d was a good tool but it was hard to maintain, hard to make evolve. For those who tried to contribute, it looked a bit like a black box. The code had serious flaws in its design. At the time, relying on Fortran was my trick to get speed. Nowadays, we can rely on numba, that yields to a much simpler install and remove the build phase. Consider switching to

Fluids2d (with an "s") https://github.com/pvthinker/Fluids2d

It's the same, in much better. Not all equations of Fluid2d are yet implemented but this will come. Same for the experiments, only a handful is proposed but the list will expand. On the numerical methods side, this code is also much better, with an extensive use of WENO reconstructions. Fluid2d systematically integrates the momentum equation in vorticity- stream-function and has no way to compute the pressure. This is no longer true. Most of Fluids2d equations are formulated with an explicit pressure.