[Plugins] : Independent Test Solution for plugins

This is more like a way or solution request for plugins to independently tests with docsify. Currently, the official plugins and most of the third-party plugins (all of them which I saw) don't have test for their plugins. Unit testing for the logic method of a plugin can be done seamlessly but for integration testing with docsify core, it's quite tough from my end.

This is required as in future release there can be some changes in the core regarding the compiler part or the hooks part or any other changes. And it is to ensure that plugins don't break.

This issue is to document the testing guide for the plugins independently. As I am not so good with testing this deep I can't document that myself.

You can either submit a PR in this repo regarding updating the docs about testing the plugins. Before submitting PR, it would be nice to have a comment here about your approach and also to have a demo by either testing any plugins from this repo or any other plugin.