accessing segments and knots

[AbiSo]

I needed to access the segments and knots from the NaturalSpline, because I am using the library to compute these values so I can re-use them later on in a different context. For that I added functions

NaturalSplineCommon::segments() const
NaturalSplineCommon::knots() const

Additionally the members variables have been renamed:

NaturalSplineCommon::mSegments;
NaturalSplineCommon::mKnots;

Find attached the patch to make the modification:

NaturalSpline_segments_knots.diff.zip

Maybe it's worth extended the interface such that this kind of information is accessible in general way. This patch just does it for the natural spline.