Convert Minecraft map marker definitions

DynMap markers.yml contains markers from all worlds, choose one.

One set name per line.

The placeholder %icon% is replaced with the icon name.

BlueMap POI markers support an optional icon offset, called anchor. This configuration option uses JSON syntax to map DynMap icon names to BlueMap anchors. Fractions will be rounded to the nearest integer. Optionally you can use the icon name * to specify a default anchor for all POI marker icons.
Imagemagick's identify tool can calculate the center of your icons, e.g. (don't forget to remove the last trailing comma from the output if you use this command):

identify -format '"%t": {"x": %[fx:w/2], "y": %[fx:h/2]},\n' *.png

Useful for debugging and editing markers.

Use line breaks and spaces to make the output more readable and easier to manually edit.

Add a commented-out section to the output that includes conversion statistics and warning messages if applicable.