Inherit min/max scale from service

I think this makes a good ‘micro’ plugin candidate (as opposed to bolting it on to esri-leaflet-renderers) for a couple reasons

1. minScale and maxScale are not part of the drawing options within the FeatureLayer metadata
2. its trivial enough that it would be well suited as a reference in much needed plugin development documentation.

at the very least it would be cool to have a sample which shows how to retrieve the information using FeatureLayer.metadata().

featureLayer.metadata(function(error, metadata){
  // convert metadata.minScale to zoom level
  featureLayer.options.minZoom = minZoom
  featureLayer.addTo(map);
});

related: https://gis.stackexchange.com/questions/7430/what-ratio-scales-do-google-maps-zoom-levels-correspond-to/81390#81390

[zachatrocity]

Great, thank you so much!

[jgravois]

@zachatrocity no worries.

// use scale to calculate level
level = Math.log(591657550.500000 / scale) / Math.log(2) + 1

this is the inverse of the StackExchange formula i linked to earlier:

// use level to calculate scale
scale = 591657550.500000 / Math.pow(2, level - 1)

ref: https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Math/log