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

examples/Console/Charts/Program.cs

@@ -1,21 +1,42 @@
 using Spectre.Console;
+using Spectre.Console.Rendering;
 
-namespace InfoExample
+namespace Charts
 {
     public static class Program
     {
         public static void Main()
         {
-            var chart = new BarChart()
+            // Render a bar chart
+            AnsiConsole.WriteLine();
+            Render("Fruits per month", new BarChart()
                 .Width(60)
                 .Label("[green bold underline]Number of fruits[/]")
                 .CenterLabel()
                 .AddItem("Apple", 12, Color.Yellow)
                 .AddItem("Orange", 54, Color.Green)
-                .AddItem("Banana", 33, Color.Red);
+                .AddItem("Banana", 33, Color.Red));
 
+            // Render a breakdown chart
             AnsiConsole.WriteLine();
-            AnsiConsole.Render(chart);
+            Render("Languages", new BreakdownChart()
+                .FullSize()
+                .Width(60)
+                .ShowAsPercentages()
+                .AddItem("SCSS", 37, Color.Red)
+                .AddItem("HTML", 28.3, Color.Blue)
+                .AddItem("C#", 22.6, Color.Green)
+                .AddItem("JavaScript", 6, Color.Yellow)
+                .AddItem("Ruby", 6, Color.LightGreen)
+                .AddItem("Shell", 0.1, Color.Aqua));
+        }
+
+        private static void Render(string title, IRenderable chart)
+        {
+            AnsiConsole.Render(
+                new Panel(chart)
+                    .Padding(1, 1)
+                    .Header(title));
         }
     }
 }