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/IRenderable.cs

@@ -0,0 +1,26 @@
+using System.Collections.Generic;
+
+namespace Spectre.Console.Rendering
+{
+    /// <summary>
+    /// Represents something that can be rendered to the console.
+    /// </summary>
+    public interface IRenderable
+    {
+        /// <summary>
+        /// Measures the renderable object.
+        /// </summary>
+        /// <param name="context">The render context.</param>
+        /// <param name="maxWidth">The maximum allowed width.</param>
+        /// <returns>The minimum and maximum width of the object.</returns>
+        Measurement Measure(RenderContext context, int maxWidth);
+
+        /// <summary>
+        /// Renders the object.
+        /// </summary>
+        /// <param name="context">The render context.</param>
+        /// <param name="maxWidth">The maximum allowed width.</param>
+        /// <returns>A collection of segments.</returns>
+        IEnumerable<Segment> Render(RenderContext context, int maxWidth);
+    }
+}