Open
Description
In some cases, you have an awful lot of markers, and don't want to display them until sufficiently zoomed in. It would be good for a filter function to optionally return a zoom level below which the marker will not be displayed (dynmap does this on a per-set basis).
As the filterfunction currently returns (name, [optionallabel]) you could add a third [optionallevel] to the return value list and retain compatibility...
For added brownie points, having the markers coalesce into summary markers displaying how many markers in a (2^level x distance) square would be good, but probably too hard to do easily...