exemple: Extended Encoding Format (chd=e)

>>> from pygooglechart import SimpleLineChart
>>> chart = SimpleLineChart(200,200, y_range=(0, 10))
>>> chart.add_data([1.0, 2.0, 6.0, 7.0, 5.0, 1.0])
>>> chart.add_data([2.0, 5.0, 5.0, 2.0, 1.0, 2.0])
>>> chart.get_url()
'http://chart.apis.google.com/chart?cht=lc&chs=200x200&chd=e:GaMzmZszgAGa,MzgAgAMzGaMz'