Slingshot Pouch Stencil

This is a stencils that makes it easier to cut out the pouches for a slingshot.
They are modelled after these instructions on YouTube by _1611torsten_:
[How to make the fastest slingshot bands; extreme speed PART 1](https://www.youtube.com/watch?v=mwgVNwxzX0Q).
They are customizable - just comment out the size you want in the openscad file:

```
//profile_scale = 1; // for 4 cm pouch = 7 mm steel ball
profile_scale = 1.125; // for 4.5 cm pouch = 8 mm steel ball
//profile_scale = 1.25; // for 5.0 cm pouch = 10 mm steel ball
//profile_scale = 1.375; // for 5.5 cm pouch = 11+ mm steel ball
```