creating empty folders on fs

[joehand]

Right now if you archive.mkdir('/dir') it does not make the directory on the file system (dat-ecosystem-archive/dat-node#164):

var hyperdrive = require('hyperdrive')
var storage = require('dat-storage')

var archive = hyperdrive(storage('./test'), {latest: true})
archive.mkdir('/my-dir', function (err) {
  console.log(err)
})