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/calendar.md

@@ -6,6 +6,8 @@ Highlights:
     - Include highlighted events.
     - Culture aware.
     - Custom headers.
+Reference: T:Spectre.Console.Calendar
+
 ---
 
 The `Calendar` is used to render a calendar to the terminal.