Fix: Add line break between description and extra when rendering props

Original PR styleguidist#290

Fix: Add line break between description and extra when rendering props (

styleguidist#290)

Fix: Move es6-object-assign to dependencies

Fix: Add es6-object-assign polyfill to support IE11 (styleguidist#285)

Changelog: 🚀

## New feature

### Components public methods

Show component public methods in the style guide, the same way as props. Tag your method with  JSDoc tag to mark mark it as public.

![](https://d3vv6lp55qjaqc.cloudfront.net/items/3z2r0b0g2I0L2b2M1D0v/Image%202017-01-10%20at%209.02.13%20AM.png)

PR styleguidist#280 by @n1313

Fix: Add webpack 2.2 support in peer deps (styleguidist#278)

Fix: Code toggle button layout in different browsers

PR styleguidist#276