draw_vertical_levels(ncfile, values, varn)
  ncfile= file to use
  values= [zlogs]:[plogs]:[title]:[graphic_kind]:[legvals]
    zlogs: zlog,dzlog
      zlog: to use logarithmic scale on the height axis ('true/false')
      dzlog: to use logarithmic scale on the difference of height between levels axis ('true/false')
    plogs: plog,dplog
      plog: to use logarithmic scale on the height axis ('true/false')
      dplog: to use logarithmic scale on the difference of height between levels axis ('true/false')
    title: title of the graph ('!' for spaces)
    graphic_kind: kind of figure (jpg, pdf, png)
    [legvals]=[locleg]|[fontsize]
      [locleg]: location of the legend (0, autmoatic)
        1: 'upper right', 2: 'upper left', 3: 'lower left', 4: 'lower right',
        5: 'right', 6: 'center left', 7: 'center right', 8: 'lower center',
        9: 'upper center', 10: 'center'
      [fontsize]: font size for the legend (auto for 12)
    varn= [varnheight],[varnpres]
      varnheight: name of the variable with the height of the vertical levels
        'WRFz': for WRF z-levels (computed as (PH + PHB)/g, from a PHB(0,i,j) = 0)
      varnpres: name of the variable with the pressure of the vertical levels ('None', for no pressure plot)
        'WRFp': for WRF p-levels (computed as P + PB, from a PHB(0,i,j) = 0)