Make width and height optional in label array

[arunkjn]

Width can be approximated by text.length() and a fixed default height can be given. This will make it easier to use.

[Fil]

this is easy to add to pull-request #3 with the following code:

      if ((typeof lab[i].width == 'undefined') || (typeof lab[i].height == 'undefined')) {
        if (typeof lab[i].width == 'undefined') lab[i].width = lab[i].name.length*6;
        if (typeof lab[i].height == 'undefined') lab[i].height = 8;
      }

width = 6 * name.length works for me, but it would be better if we could use the label object to find the label itself and measure its bounding box. Unfortunately, the way it is programmed now, we work outside the svg object.