dice pencil extender or cap

Pencils are great, however when they are used they get shorter and shorter every time they are sharpened until is is hard to hold them. So an extender makes using them way more fun if they get shorter.

While modifying my [Allen key/hex key extender](https://www.thingiverse.com/thing:2985572) to work as an extender I thought it would be great to add a dice as additional feature to the thing. Since I also have round pencils they are also supported.

The following can be adjusted:

* shape