Finds bounding box for rle volume
npm install rle-extentsrle-extents
===========
Computes a bounding box for a narrowband level set.
npm install rle-extents
``javascript
//First run length encode a bunny
var bunny = require("bunny")
var bunny_rle = require("rle-rasterize")(bunny.cells, bunny.positions)
//Compute extents of the volume
var extents = require("rle-extents")(bunny_rle)
console.log("lo=", extents[0], "hi=", extents[1])
`
* volume` is a narrowband level set
Returns A pair of 3D arrays representing the lower and upper bounds on the volume.