fill a compressed ipv6 address with zeros
npm install pad-ipv6
expand a compressed ipv6 to a 39 character representation
``var padIpv6 = require("pad-ipv6");
var padIpv6 = require("pad-ipv6");
padIpv6("fe80:685::ff:fe72:c4fa"); // 'fe80:0685:0000:0000:0000:00ff:fe72:c4fa'``