Expose shape fields

[carrascomj]

Description

Making the Shape fields public allows for surgical modifications without requiring to rebuild the Path when only changes to the color or the options of some field are desired.

Implementation

• Made all Shape attributes public.
• Added an example of changing the fill and stroke without rebuilding the path.

This works since src/plugins.rs:mesh_shapes_system is triggered by changes in the fields of a Shape.

[carrascomj]

Probably the getter methods of Shape should now be removed (?).