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/Cli/Demo/Program.cs

@@ -1,4 +1,7 @@
 using Demo.Commands;
+using Demo.Commands.Add;
+using Demo.Commands.Run;
+using Demo.Commands.Serve;
 using Spectre.Console.Cli;
 
 namespace Demo;