Add rule widget

Adds a new rule widget.
Also fixes some bugs I encountered while testing
some unrelated things in an extremely small console.

examples/Rules/Program.cs

@@ -0,0 +1,28 @@
+using Spectre.Console;
+
+namespace EmojiExample
+{
+    public static class Program
+    {
+        public static void Main(string[] args)
+        {
+            // No title
+            Render(new Rule().SetStyle("yellow"));
+
+            // Left aligned title
+            Render(new Rule("[white]Left aligned[/]").LeftAligned().SetStyle("red"));
+
+            // Centered title
+            Render(new Rule("[silver]Centered[/]").Centered().SetStyle("green"));
+
+            // Right aligned title
+            Render(new Rule("[grey]Right aligned[/]").RightAligned().SetStyle("blue"));
+        }
+
+        private static void Render(Rule rule)
+        {
+            AnsiConsole.Render(new Panel(rule).Expand().SetBorderStyle(Style.Parse("grey")));
+            AnsiConsole.WriteLine();
+        }
+    }
+}

examples/Rules/Rules.csproj

@@ -0,0 +1,15 @@
+<Project Sdk="Microsoft.NET.Sdk">
+
+  <PropertyGroup>
+    <OutputType>Exe</OutputType>
+    <TargetFramework>netcoreapp3.1</TargetFramework>
+    <IsPackable>false</IsPackable>
+    <Title>Rules</Title>
+    <Description>Demonstrates how to render horizontal rules (lines).</Description>
+  </PropertyGroup>
+
+  <ItemGroup>
+    <ProjectReference Include="..\..\src\Spectre.Console\Spectre.Console.csproj" />
+  </ItemGroup>
+
+</Project>