Auto-generate documentation for Wiki (#292)

This adds a new script utility, `Build-Wiki.ps1`, which can be used to auto-generate the documentation for the Wiki.  This uses the [PlatyPS](https://github.com/PowerShell/PlatyPS) module to generate the actual help documentation.

Relevant notes:
* This will generate the `Home.md`, `_sidebar.md`, and `_footer.md`   files for the Wiki if they don't already exist in the destination directory.
* If they do already exist, it intelligently updates the content, only replacing the parts that it generated itself (denoted with
  comments in the markdown content itself).
* At present, this is not being hooked-up to CI because I don't want to deal with storing credentials that have admin access 
to the actual repo.

Tip of the hat to @X-Guardian for the suggestion and the initial help with writing this out.

Resolves #208

Author: HowardWolosky