Fixes for the Boo scripts

Today I've worked on improving the Boo script functionality, mainly updating the methods to use the new structure (Reference instead of Point3D), adding sketch-related functionality and allowing methods to use references to previously created points instead of having to use their coordinates.

For example, the following Boo script:

s1=Sketch(5,0,0,1,2,0,0,0,0)
EnterSketch(s1)
p1=Point(s1,2,5,0)
Circle(p1,20)

s2=Sketch(5,0,0,0,5,0,0,0,5)
EnterSketch(s2)
p2=Point(s2,2,5,3)
Circle(p2,20)

EnterSketch(s1)
p3=Point(s1,10,10,0)
Circle(p3,5)

creates:

With the current version of the code it's possible to create and edit sketches and draw 2D shapes in them. Tomorrow I will complete the changes for the 2D shapes, update the help section for them and start working on the 3D commands.