Guess quantize factor from input data

[mattijn]

This PR fix #140.

When loading Topojson data from file the data its pretty normal that the data is quantised and delta-encoded beforehand.

But in this case during the toposimplification it first dequantize the arcs, then apply a simplify and then quantise again. But for the quantisation it requires a quantisation factor. If this is not set in the options it will now use an estimated guess from the input data.

The delta-encoding happens from the first coordinate of each arc, so we can check the integer length of the max coordinate-value of all arcs first coordinate.

power_estimate = len(str(int(np_arcs[:,0].max())))
quant_factor_estimate = 10 ** power_estimate