Change IAnsiConsole to render IRenderable

This makes it possible for encoders to output better representation
of the actual objects instead of working with chopped up segments.

* IAnsiConsole.Write now takes an IRenderable instead of segments
* Calculating cell width does no longer require a render context
* Removed RenderContext.LegacyConsole
* Removed RenderContext.Encoding
* Added Capabilities.Unicode

src/Spectre.Console/AnsiConsole.Rendering.cs

@@ -1,3 +1,4 @@
+using System;
 using Spectre.Console.Rendering;
 
 namespace Spectre.Console
@@ -13,7 +14,12 @@ namespace Spectre.Console
         /// <param name="renderable">The object to render.</param>
         public static void Render(IRenderable renderable)
         {
-            Console.Render(renderable);
+            if (renderable is null)
+            {
+                throw new ArgumentNullException(nameof(renderable));
+            }
+
+            Console.Write(renderable);
         }
     }
 }