Add support for bar charts

Closes #103

src/Spectre.Console.Tests/Expectations/BarChartTests.Should_Render_Correctly.verified.txt

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+                          Number of fruits                  
+ Apple  ████████ 12                                         
+Orange  █████████████████████████████████████████████████ 54
+Banana  ████████████████████████████ 33                     

src/Spectre.Console.Tests/Unit/BarChartTests.cs

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+using System.Threading.Tasks;
+using VerifyXunit;
+using Xunit;
+
+namespace Spectre.Console.Tests.Unit
+{
+    [UsesVerify]
+    public sealed class BarChartTests
+    {
+        [Fact]
+        public async Task Should_Render_Correctly()
+        {
+            // Given
+            var console = new PlainConsole(width: 80);
+
+            // When
+            console.Render(new BarChart()
+                .Width(60)
+                .Label("Number of fruits")
+                .AddItem("Apple", 12)
+                .AddItem("Orange", 54)
+                .AddItem("Banana", 33));
+
+            // Then
+            await Verifier.Verify(console.Output);
+        }
+    }
+}