Clean up public API

* Make things a bit more consistent
* Add extension methods to configure things like tables, panels and grids.

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

@@ -0,0 +1,81 @@
+namespace Spectre.Console
+{
+    /// <summary>
+    /// Contains extension methods for <see cref="IAlignable"/>.
+    /// </summary>
+    public static class AlignableExtensions
+    {
+        /// <summary>
+        /// Sets the alignment for an <see cref="IAlignable"/> object.
+        /// </summary>
+        /// <typeparam name="T">The alignable object type.</typeparam>
+        /// <param name="obj">The alignable object.</param>
+        /// <param name="alignment">The alignment.</param>
+        /// <returns>The same instance so that multiple calls can be chained.</returns>
+        public static T SetAlignment<T>(this T obj, Justify alignment)
+            where T : class, IAlignable
+        {
+            if (obj is null)
+            {
+                throw new System.ArgumentNullException(nameof(obj));
+            }
+
+            obj.Alignment = alignment;
+            return obj;
+        }
+
+        /// <summary>
+        /// Sets the <see cref="IAlignable"/> object to be left aligned.
+        /// </summary>
+        /// <typeparam name="T">The alignable type.</typeparam>
+        /// <param name="obj">The alignable object.</param>
+        /// <returns>The same instance so that multiple calls can be chained.</returns>
+        public static T LeftAligned<T>(this T obj)
+            where T : class, IAlignable
+        {
+            if (obj is null)
+            {
+                throw new System.ArgumentNullException(nameof(obj));
+            }
+
+            obj.Alignment = Justify.Left;
+            return obj;
+        }
+
+        /// <summary>
+        /// Sets the <see cref="IAlignable"/> object to be centered.
+        /// </summary>
+        /// <typeparam name="T">The alignable type.</typeparam>
+        /// <param name="obj">The alignable object.</param>
+        /// <returns>The same instance so that multiple calls can be chained.</returns>
+        public static T Centered<T>(this T obj)
+            where T : class, IAlignable
+        {
+            if (obj is null)
+            {
+                throw new System.ArgumentNullException(nameof(obj));
+            }
+
+            obj.Alignment = Justify.Center;
+            return obj;
+        }
+
+        /// <summary>
+        /// Sets the <see cref="IAlignable"/> object to be right aligned.
+        /// </summary>
+        /// <typeparam name="T">The alignable type.</typeparam>
+        /// <param name="obj">The alignable object.</param>
+        /// <returns>The same instance so that multiple calls can be chained.</returns>
+        public static T RightAligned<T>(this T obj)
+            where T : class, IAlignable
+        {
+            if (obj is null)
+            {
+                throw new System.ArgumentNullException(nameof(obj));
+            }
+
+            obj.Alignment = Justify.Right;
+            return obj;
+        }
+    }
+}