Customizable number or text insert

Remixed version of the [Customizable tag](https://www.thingiverse.com/thing:2781647) by b2vn. I have removed the hole at the top and added a stem to the bottom instead.

If you want to customize this i would strongly suggest to download OpenSCAD and edit the file locally, since the thingiverse customize doesn't seem to be able to display the text and is very sluggish overall.

In my example I did not cut the number all the way through to the backside but instead left some layers to be able to fill the numbers with nail polish. You are however still able to to that by changing the INDENT parameter to a value equal or higher than the THICKNESS parameter.

Note that the center piece (which you can enable by setting the CENTER_PIECE parameter to a value higher than 0) only works correctly with single digits or letters, since i have not added any logic to move or duplicate the center piece.