v5.6.0

This release includes:

• various bug fixes;
• the robustification of isosurface discretization, more particularely in multi-material mode;
• internal modifications of the analysis to support the parallel surface analysis in ParMmg;
• a new possible argument for the -3dMedit command line argument: now -3dMedit 3 allow to pass from a 2D mesh saved in 3D into a "true" 2D Medit file.