A function to drape linestring with TIN

[komzpa]

per discussion with pramsey:

• should take a TIN and linestring, promote linestring to have Z dimension with default of 0;

• for all covered points of linestring, set Z by interpolating on triangle;

• for all spots where linestring hits edge of triangle, generate intermediate points with Z from triangle.

• all values outside of TIN should be unchanged.