Speed up evaluation of NURBS curves by use of subdivision into Bezier segments

[portnov]

Evaluation of Bezier curves is much faster than evaluation of generic NURBS curves. But, any NURBS curve can be split up into list of Bezier segments.
For now, this is implemented for non-rational curves only.
And anyway this has to be extensively tested.

Preflight checklist

Put an x letter in each brackets when you're done this item:

• Code changes complete.
• Code documentation complete.
• Documentation for users complete (or not required, if user never sees these changes).
• Manual testing done.
• Unit-tests implemented.
• Ready for merge.

[portnov]

Why this is not merged yet:
This new implementation has much more efficient curve.evaluate_array() method, i.e. when we have one Curve object, we can calculate lots of points at once very quickly.
However, many NURBS algorithms, such as intersection of curves, require not evaluation of many points at once, but instead: 1) evaluation at one point; 2) control points manipulation primitives, such as "insert knot" or "split curve in two". And these primitives are slower in new implementation.

An idea how to proceed: for "Bezier In" and "NURBS Input" nodes, add possibility to use new implementation (add new item to "Implementation" parameter). So that if the user knows he has to calculate many points on the curve and not do more complex manipulations, he can use new implementation. Also maybe add new node "Convert NURBS Curve Implementation".