Improved the semi-automatic "Snap-To-Point" function and corresponding UI.
This is mostly due to better matching and usage of Splines.

Initial pass: user quickly clicks on desired location and proceeds WITHOUT correction

On the second, manual pass, user simply drags the control points (about 5-6) in this example and contour adjusts.

Implemented general  Cubic Hermite Splines 2D function.  It supports several types of splines {CARDINAL,FinalDiff,Catmull-ROM}
The challenge was to implement it so it matches exactly the Microsoft's GDI+ implementation in DrawCurve() - this was achieved.

Function can be easily expanded to 3D.