Release of VEMLAB 2.4.1

>>  From VEMLAB 2.4 to VEMLAB 2.4.1:

• Fix some bugs in create_polygonal_mesh.m
• Fix several bugs in the writing of output files. Affected functions:
  postprocess_numerical_solution_linelast2d.m
  write_solution_txt_linelast2d.m
  plot_numerical_solution_poisson2d.m
  postprocess_numerical_solution_poisson2d.m
  write_solution_CPP_poisson2d.m
  write_solution_txt_poisson2d.m
  write_solution_GiD_poisson2d.m
• Optimize function T3toPolyMesh.m