StretchSection example files

Try the app at https://stretch.parametricfab.com/

The before file is the sample bracket included in the app. It has three holes.
The after file has 20 mm added to a 40 mm section along X.

To reproduce it:
1. Open stretchsection-demo-before.stl.
2. Set the stretch direction to X.
3. Set Start to 30 mm and End to 70 mm.
4. Set the length change to +20 mm.
5. Keep the start side fixed, then export the preview.

The selected section goes from 40 mm to 60 mm. The total X size goes from
about 101.20 mm to 121.20 mm. The ends keep their shape and size. The middle
hole stretches because it is inside the selected section.

These are digital examples. More checks with real prints are still needed.

The sample models and the project code are provided under the MIT License.
