Docs redesign (#728)

* Adding a dark mode
* Adding reference for types to summary pages
* Adding API Reference
* Adding modifiers to methods/fields/etc
* Minimizing files input
* Caching a lot of the output pages
* Cache only for each execution
* Adding API references to existing docs

docs/input/widgets/canvas-image.md

@@ -1,6 +1,7 @@
 Title: Canvas Image
 Order: 70
 Description: "Use *ImageSharp* to parse images and render them as Ascii art to the console."
+Reference: T:Spectre.Console.CanvasImage
 ---
 
 To add [ImageSharp](https://github.com/SixLabors/ImageSharp) superpowers to