Add React Hooks

[macabeus]

fluent-react provides a simpler way to use fluent on a React application, but it's laking a built-in function to get messages using react hooks.
Currently is possible to get the messages just using a HOC using withLocalization or with <Localized />.

It's a similar approach that react-i18next already do.

Sometimes is better just to call a function instead of increasing the JSX code wrapping each message with the <Localized /> component. For example, here:

<Localized id="nav-campaigns">
  <span></span>
</Localized>

<!-- would be just... -->
<span>{t('nav-campaigns')}</span>

Related: #182

[stasm]

Thanks for your work on this, @macabeus! I released @fluent/react 0.13 last week with your changes: https://github.com/projectfluent/fluent.js/blob/master/fluent-react/CHANGELOG.md#fluentreact-0130-july-2-2020. I also added a note about useLocalization on the wiki: https://github.com/projectfluent/fluent.js/wiki/useLocalization