Bevel Factor Mapping

Bevel Factor Mapping

Bevel Factor Mapping allows to control the relation between bevel factors
(number between 0 and 1) and the rendered start and end point of a beveled
spline.

There are three options: "Resolution", "Segments", "Spline". "Resolution"
option maps bevel factors as it was done < 2.71, "Spline" and "Segments"
are new.

* "Resolution“: Map the bevel factor to the number of subdivisions of a
  spline (U resolution).
* "Segments“: Map the bevel factor to the length of a segment and to the
  number of subdivisions of a segment.
* "Spline": Map the bevel factor to the length of a spline.

Reviewers: yakca, sergey, campbellbarton

CC: sanne
Differential Revision: https://developer.blender.org/D294