Plot nurbs objects for NURBS toolbox

Updated 'nrbplot' function from NURBS toolbox. Allows to pass parameters/value pairs for plotting.

% Examples:
%
% The two statements below are equivalent and plot a nurbs surface with
% lighting gouraud.
You need the NURBS toolbox for use of this function.

Example:

nurbs=nrbtestsrf;
h=nrbplot(nurbs,50,50],'FaceColor','r','EdgeColor','k','FaceLighting','gouraud');
light

h=nrbplot(nurbs,linspace(0,1,50),linspace(0,1,50)},'FaceColor','r','EdgeColor','k','FaceLighting','gouraud');
light