Add live display support

This commit also adds functionality to LiveRenderable that should
fix some problems related to vertical overflow.

Closes #316
Closes #415

src/Spectre.Console/Extensions/AnsiConsoleExtensions.Live.cs

@@ -0,0 +1,32 @@
+using System;
+using Spectre.Console.Rendering;
+
+namespace Spectre.Console
+{
+    /// <summary>
+    /// Contains extension methods for <see cref="IAnsiConsole"/>.
+    /// </summary>
+    public static partial class AnsiConsoleExtensions
+    {
+        /// <summary>
+        /// Creates a new <see cref="LiveDisplay"/> instance for the console.
+        /// </summary>
+        /// <param name="console">The console.</param>
+        /// <param name="target">The target renderable to update.</param>
+        /// <returns>A <see cref="LiveDisplay"/> instance.</returns>
+        public static LiveDisplay Live(this IAnsiConsole console, IRenderable target)
+        {
+            if (console is null)
+            {
+                throw new ArgumentNullException(nameof(console));
+            }
+
+            if (target is null)
+            {
+                throw new ArgumentNullException(nameof(target));
+            }
+
+            return new LiveDisplay(console, target);
+        }
+    }
+}

src/Spectre.Console/Extensions/LiveDisplayExtensions.cs

@@ -0,0 +1,65 @@
+using System;
+
+namespace Spectre.Console
+{
+    /// <summary>
+    /// Contains extension methods for <see cref="LiveDisplay"/>.
+    /// </summary>
+    public static class LiveDisplayExtensions
+    {
+        /// <summary>
+        /// Sets whether or not auto clear is enabled.
+        /// If enabled, the live display will be cleared when done.
+        /// </summary>
+        /// <param name="live">The <see cref="LiveDisplay"/> instance.</param>
+        /// <param name="enabled">Whether or not auto clear is enabled.</param>
+        /// <returns>The same instance so that multiple calls can be chained.</returns>
+        public static LiveDisplay AutoClear(this LiveDisplay live, bool enabled)
+        {
+            if (live is null)
+            {
+                throw new ArgumentNullException(nameof(live));
+            }
+
+            live.AutoClear = enabled;
+
+            return live;
+        }
+
+        /// <summary>
+        /// Sets the vertical overflow strategy.
+        /// </summary>
+        /// <param name="live">The <see cref="LiveDisplay"/> instance.</param>
+        /// <param name="overflow">The overflow strategy to use.</param>
+        /// <returns>The same instance so that multiple calls can be chained.</returns>
+        public static LiveDisplay Overflow(this LiveDisplay live, VerticalOverflow overflow)
+        {
+            if (live is null)
+            {
+                throw new ArgumentNullException(nameof(live));
+            }
+
+            live.Overflow = overflow;
+
+            return live;
+        }
+
+        /// <summary>
+        /// Sets the vertical overflow cropping strategy.
+        /// </summary>
+        /// <param name="live">The <see cref="LiveDisplay"/> instance.</param>
+        /// <param name="cropping">The overflow cropping strategy to use.</param>
+        /// <returns>The same instance so that multiple calls can be chained.</returns>
+        public static LiveDisplay Cropping(this LiveDisplay live, VerticalOverflowCropping cropping)
+        {
+            if (live is null)
+            {
+                throw new ArgumentNullException(nameof(live));
+            }
+
+            live.Cropping = cropping;
+
+            return live;
+        }
+    }
+}

src/Spectre.Console/Extensions/TableColumnExtensions.cs

@@ -8,11 +8,55 @@ namespace Spectre.Console
     /// </summary>
     public static class TableColumnExtensions
     {
+        /// <summary>
+        /// Sets the table column header.
+        /// </summary>
+        /// <param name="column">The table column.</param>
+        /// <param name="header">The table column header markup text.</param>
+        /// <returns>The same instance so that multiple calls can be chained.</returns>
+        public static TableColumn Header(this TableColumn column, string header)
+        {
+            if (column is null)
+            {
+                throw new ArgumentNullException(nameof(column));
+            }
+
+            if (header is null)
+            {
+                throw new ArgumentNullException(nameof(header));
+            }
+
+            column.Header = new Markup(header);
+            return column;
+        }
+
+        /// <summary>
+        /// Sets the table column header.
+        /// </summary>
+        /// <param name="column">The table column.</param>
+        /// <param name="header">The table column header.</param>
+        /// <returns>The same instance so that multiple calls can be chained.</returns>
+        public static TableColumn Header(this TableColumn column, IRenderable header)
+        {
+            if (column is null)
+            {
+                throw new ArgumentNullException(nameof(column));
+            }
+
+            if (header is null)
+            {
+                throw new ArgumentNullException(nameof(header));
+            }
+
+            column.Footer = header;
+            return column;
+        }
+
         /// <summary>
         /// Sets the table column footer.
         /// </summary>
         /// <param name="column">The table column.</param>
-        /// <param name="footer">The table column markup text.</param>
+        /// <param name="footer">The table column footer markup text.</param>
         /// <returns>The same instance so that multiple calls can be chained.</returns>
         public static TableColumn Footer(this TableColumn column, string footer)
         {