Switch to use decorator API

[pocka]

Use decorator API instead of manual decoration (component wrapping?).
Close #73

// before
storiesOf('...')
  .add('...', withInfo({
    // options here
  })(() => ({
    template: 'story'
  })))

// after
storiesOf('...')
  .addDecorator(withInfo)
  .add('...', () => ({
    template: 'story'
  }), {
    info: {
      // options here
    }
  })

This change enables us to work with addon-knobs (if you're using >= @storybook/[email protected]).

https://deploy-preview-74--storybook-addon-vue-info.netlify.com/?panelRight=1

[pocka]

Build breaks due to yesterday release of Terser. (storybook -> webpack -> Terser)
Waiting for a new release...

[blocka]

When I do this TS complains because withInfo is not a StoryDecorator