Restore codefund plugin to plugin list.

[trusktr]

The issue it had with IE 11 is fixed: njleonzhang/docsify-plugin-codefund#6

But if any plugin has browser compatibility issue, perhaps we shouldn't remove it. After all we aren't testing all of them. We should state that third party plugins come with no Docsify guarantees.

[anikethsaha]

codefund has been shutdown. the plugin will become non functional soon. So I guess it wont make sense to add again as the service itself is shutdown.

[trusktr]

codefund has been shutdown

oooh, I didn't realize that part! :) There was no point in fixing it then. 😆 EDIT: looks like it just happened due to the economic downturn of Coronavirus. Dang, that's too bad!