ES6 module import error fix #14

[jessy1092]

Support ES6 export and import. Relative #14

Now could use like

import {Button} from 'react-semantify';

or

import * as Semantify from 'react-semantify';
let {Button} = Semantify;

or es5

var Button = require('react-semantify').Button;

Not support:

import Semantify from 'react-semantify';
let {Button} = Semantify;