added an item type

[GabrielDelepine]

I created constants but unfortunately I cannot export them because we need to keep the compatibility with the actual implementation

const dirTree = require('directory-tree');

When Node will natively support ES6 import, it can be interesting to do

in lib/directory-tree.js

export constants
export default directoryTree

import directoryTree, { constants } from 'directory-tree'

Closing issue #26

[mihneadb]

Awesome, thanks! You need to rebase on the last master though.

[mihneadb]

Let's keep the semicolon here pls.

[GabrielDelepine]

Hi @mihneadb, the PR is ready to be merge. Do you think I should make more modification ?

[mihneadb]

Thanks!