let k = require('./lib/index');
let center = { a: 1, b: 2 },
neighbor = { a: 1, c: 4 },
neighbors = [
{a: 1, c: 5, d: 3},
{a: 1, c: 4}
];
k.neighbor( center, neighbor ); // return 2 for distance from center to neighbor
neighbor = { a: 1, b: 2 };
k.neighbor( center, neighbor ); // return 0 for distance from center to neighbor
k.neighbors( center, neighbors ); // see how it works
