Add breakdown chart support

This also cleans up the bar chart code slightly and fixes
some minor bugs that were detected in related code.

Closes #244

src/Spectre.Console/IHasCulture.cs

@@ -10,6 +10,6 @@ namespace Spectre.Console
         /// <summary>
         /// Gets or sets the culture.
         /// </summary>
-        CultureInfo Culture { get; set; }
+        CultureInfo? Culture { get; set; }
     }
 }