Move built components to the root of the module on pubshish

[narqo]

Currently, one has to specify a rather long path to import a component, e.g. react-islands/components/Button. As we aren't going to add any other staff to the library except components, it's might be handy if the user could import modules in a more concise way:

import Button from 'react-islands/Button';

We might genereate an index.js that exports all modules as well,

import { Button, Checkbox } from 'react-islands';

but I'd prefer to not recommended this way of usage, as it led to bundling the whole library to the user's project, even if only some components were used.

/cc @vodkabears @pasaran

[vodkabears]

index.js is ok, if module bundler supports a tree-shaking.

I like the standart lib folder:
import Button from 'react-islands/lib/Button';

[narqo]

JFI: index.js was added to v0.5.0.