add_mesh_round_cube.py

This was a problem with the BezTriple type.
Write access to BezTriple via 'pt' member did not work.

Preferred method to access BPy type members, especially for
write access, is via get*/set* methods.

BezTriple.setPoints() will accept x,y coordinates as either
a tuple or a list.

Updated BezTriple section of Ipo module doc.