Add support for DocC documentation and tutorials

[andrew-winn-br]

I think it would be cool if we support DocC documentation as well as the tutorial system. In particular I think the tutorials would be a good enhancement for the examples.

https://developer.apple.com/documentation/docc/tutorial-syntax

[andrew-winn-br]

If no one has a problem with this, this is something I would like to tackle.

[wmcginty]

It's all you @andrew-winn-br !