Nurbs birail update 2

[portnov]

Add a parameter which controls rotation of profile curves.

• Path Normal Average. The node will try to place profile curves so that
  they will lie in normal planes of both path curves. Since normal planes of
  two path curves can differ, the node will calculate average normal plane.
• Path 1 Normal. The node will place profile curves so that they lie in
  normal plane of the first path curve.
• Path 2 Normal. The node will place profile curves so that they lie in
  normal plane of the second path curve.
• By profile. The node will try to place profile curves so that they be
  parallel to initial location of the path curve. This is not always
  possible, but the node will try to keep it as parallel as possible.

The default option is Path Normal Average.

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.

[rendetto]

Thank you for this cool update! I'll start exploring the options.
What settings will recreate the behavior of the node before the update?

[portnov]

The default ones. We always try to preserve backward compatibility.

[rendetto]

Perfect! Thank you!