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

examples/Console/Tables/Program.cs

@@ -1,3 +1,4 @@
+using System.Diagnostics;
 using Spectre.Console;
 
 namespace TableExample