Add text overflow support

Closes #61

src/Spectre.Console/Rendering/Traits/Extensions/OverflowableExtensions.cs

@@ -0,0 +1,80 @@
+using System;
+
+namespace Spectre.Console
+{
+    /// <summary>
+    /// Contains extension methods for <see cref="IOverflowable"/>.
+    /// </summary>
+    public static class OverflowableExtensions
+    {
+        /// <summary>
+        /// Folds any overflowing text.
+        /// </summary>
+        /// <typeparam name="T">An object implementing <see cref="IOverflowable"/>.</typeparam>
+        /// <param name="obj">The overflowable object instance.</param>
+        /// <returns>The same instance so that multiple calls can be chained.</returns>
+        public static T Fold<T>(this T obj)
+            where T : class, IOverflowable
+        {
+            if (obj is null)
+            {
+                throw new ArgumentNullException(nameof(obj));
+            }
+
+            return SetOverflow(obj, Overflow.Fold);
+        }
+
+        /// <summary>
+        /// Crops any overflowing text.
+        /// </summary>
+        /// <typeparam name="T">An object implementing <see cref="IOverflowable"/>.</typeparam>
+        /// <param name="obj">The overflowable object instance.</param>
+        /// <returns>The same instance so that multiple calls can be chained.</returns>
+        public static T Crop<T>(this T obj)
+            where T : class, IOverflowable
+        {
+            if (obj is null)
+            {
+                throw new ArgumentNullException(nameof(obj));
+            }
+
+            return SetOverflow(obj, Overflow.Crop);
+        }
+
+        /// <summary>
+        /// Crops any overflowing text and adds an ellipsis to the end.
+        /// </summary>
+        /// <typeparam name="T">An object implementing <see cref="IOverflowable"/>.</typeparam>
+        /// <param name="obj">The overflowable object instance.</param>
+        /// <returns>The same instance so that multiple calls can be chained.</returns>
+        public static T Ellipsis<T>(this T obj)
+            where T : class, IOverflowable
+        {
+            if (obj is null)
+            {
+                throw new ArgumentNullException(nameof(obj));
+            }
+
+            return SetOverflow(obj, Overflow.Ellipsis);
+        }
+
+        /// <summary>
+        /// Sets the overflow strategy.
+        /// </summary>
+        /// <typeparam name="T">An object implementing <see cref="IOverflowable"/>.</typeparam>
+        /// <param name="obj">The overflowable object 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 T SetOverflow<T>(this T obj, Overflow overflow)
+            where T : class, IOverflowable
+        {
+            if (obj is null)
+            {
+                throw new ArgumentNullException(nameof(obj));
+            }
+
+            obj.Overflow = overflow;
+            return obj;
+        }
+    }
+}