Automatically convert GitHub Wikis to MarkBind sites

[Xenonym]

Tell us about your environment

• MarkBind Version: 1.17.2

Rationale: GitHub Wikis are used commonly for project documentation (eg. Angular.JS, d3). It would be viable to support automatic conversions for wikis as they are all flat directories of Markdown files in a Git repository, which should be relatively simple to implement.

In addition, we can also convert a wiki's custom footers and sidebars (_Footer.md, _Sidebar.md) to our corresponding footer.md and site-nav.md. Additionally, many wikis use a sidebar that is generated by github-wiki-sidebar, whose output can cleanly translate to our own site-nav.md:

* [Installation](./Installation)
* [Roadmap](./Roadmap)
* [Usage](./Usage)
  * [Command line modifiers](./Usage%3A-Command-line-modifiers)
  * [Default mode (enquire)](./Usage%3A-Default-mode-(enquire))
  * [Tutorial mode](./Usage%3A-Tutorial-mode)
* [Examples](./Examples)

Alternatively, we can parse the file listing of the GitHub wiki to generate the site nav.

[yamgent]

Good idea, looking forward to your implementation. 👍