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/prompts/selection.md

@@ -1,6 +1,9 @@
 Title: Selection
 Order: 1
 Description: "The **SelectionPrompt** can be used when you want the user to select a single item from a provided list."
+Reference: 
+    - T:Spectre.Console.SelectionPrompt`1
+    - M:Spectre.Console.AnsiConsole.Prompt``1(Spectre.Console.IPrompt{``0})
 ---
 
 The `SelectionPrompt` can be used when you want the user to select