Imports NetGen .vol files

 USAGE

  function [mesh regions region_names boundaries boundary_names] = importNetGenMesh(filename_vol, preserve_boundary)

 INPUT

  filename:            filename ('.vol', file must be in ASCII format)

 OPTIONAL INPUT

  preserve_boundary:   Set to false to build a new boundary (BH) for the
                       mesh.

                       This ignores the boundary definition in the file.
                       The new boundary is build so that there no boundary
                       elements between elements. If a region of the
                       boundary cannot be found from the new boundary, the
                       corresponding entry in 'boundaries' contains indices
                       to nodes instead.

 OUTPUT

  mesh:                a structure that contains coordinates (r), 
                       elements (H, indices to r) and
                       boundary elements (BH, indices to r)
                       

  regions:             the regions (indices to H) in the vol file as cell
                       array

  region_names:        names of the regions as a cell array. Indexing is
                       the same as in 'regions'.

  boundaries: 		    same as regions, but for boundaries (indices to BH)

  boundary_names:	    same as region_names, but for boundaries


  EXAMPLE:

 [vmcmesh regions region_names boundaries boundary_names] = importNetGenMesh('square_with_two_circles.vol', false);
 background = cell2mat(regions(find(strcmp(region_names,'background'))));
 circles = cell2mat(regions(find(strcmp(region_names,'circles'))));
 lightsource1 = cell2mat(boundaries(find(strcmp(boundary_names,'lightsource'))));

 vmcboundary.lightsource(lightsource1) = {'cosinic'};
 vmcboundary.absorption_coefficient(background) = 0.01;
 vmcboundary.absorption_coefficient(circles) = 0.02;

 This function is provided with ValoMC