Smooth Curves for Gtk Chart Component

I recently upgraded my Gtk Graph/Charting component to draw smooth curves between data points when requested. This minor updates uses cubic splines to draw curves that touch every data point in the series being drawn. This is different from plotting a trend or curve fitting, that would mean trying to fit a curve of some degree to the data points.

Smooth curves

Smooth curves applied to bounding area plot

The above images show that not only are smooth curves applied to line plots, but also area, and bounding area plots.

So what about the more complex task of curve fitting ? I've laid some groundwork for that in response to some requests so expect to see it in the future.