Customized version of the minetestmapper utilities for voxelibre.

This is *not* the full minetestmapper, just the mod + script to generate colors.txt

Original version:
https://github.com/minetest/minetestmapper/tree/master/util/

To use minetestmapper, first install minetestmapper (e.g., "apt install minetestmapper").

Example call:
```
minetestmapper -i worlds/myworld --colors games/voxelibre/tools/colors.txt --drawalpha -o /tmp/map.png
```
