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/Widgets/Charts/BreakdownBar.cs

@@ -0,0 +1,42 @@
+using System;
+using System.Collections.Generic;
+using System.Linq;
+using Spectre.Console.Rendering;
+
+namespace Spectre.Console
+{
+    internal sealed class BreakdownBar : Renderable
+    {
+        private readonly List<IBreakdownChartItem> _data;
+
+        public int? Width { get; set; }
+
+        public BreakdownBar(List<IBreakdownChartItem> data)
+        {
+            _data = data ?? throw new ArgumentNullException(nameof(data));
+        }
+
+        protected override Measurement Measure(RenderContext context, int maxWidth)
+        {
+            var width = Math.Min(Width ?? maxWidth, maxWidth);
+            return new Measurement(width, width);
+        }
+
+        protected override IEnumerable<Segment> Render(RenderContext context, int maxWidth)
+        {
+            var width = Math.Min(Width ?? maxWidth, maxWidth);
+
+            // Chart
+            var maxValue = _data.Sum(i => i.Value);
+            var items = _data.ToArray();
+            var bars = Ratio.Distribute(width, items.Select(i => Math.Max(0, (int)(width * (i.Value / maxValue)))).ToArray());
+
+            for (var index = 0; index < items.Length; index++)
+            {
+                yield return new Segment(new string('█', bars[index]), new Style(items[index].Color));
+            }
+
+            yield return Segment.LineBreak;
+        }
+    }
+}