Creates a mesh structure with a rectangular geometry

 DESCRIPTION:

       This can function can be used to create a rectangular mesh (2D)

 USAGE:

       vmcmesh = createRectangularMesh(xsize, ysize, step)
       
 INPUT:

       xsize        - rectangle width [mm]
       ysize        - rectangle height [mm]
       dh           - width and height of each triangle in the mesh

 OUTPUT:

       vmcmesh      - mesh structure, contains the geometry of the system

 SEE ALSO:
 
                      createCircularMesh, createGridMesh

 This function is provided with ValoMC