enhanced sidebar

1. using '.sidebar' for main sidebar, using '.app-sub-sidebar' for docs sidebar.

2. add '+/-' sign before link.

3. when you click at '+/-' button, you can expand/collapse the item.

4. when you click the link, the main page sync scroll and heighlight.

5. when you scroll the main page, the '.app-sub-sidebar' sync scroll and auto expand/collapse.

source code

https://github.com/vagra/docsify
branch: sidebar

demo site

https://kepan.org/alpha/#/kepan/
(this is a temp link, will be closed in the future)

https://kepan.org/docsify/
this is using modify version of docsify, support for up to 108 levels heading.

If you feel good, you can merge my code to your project.