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

examples/Console/Columns/User.cs

@@ -1,6 +1,6 @@
 using System.Collections.Generic;
 
-namespace Spectre.Console.Examples;
+namespace Columns;
 
 public sealed class User
 {