Add canvas and image support

Adds support for drawing "pixels" and displaying
images in the terminal.

examples/Canvas/Program.cs

@@ -0,0 +1,36 @@
+using SixLabors.ImageSharp.Processing;
+using Spectre.Console;
+using Spectre.Console.Rendering;
+
+namespace CanvasExample
+{
+    public static class Program
+    {
+        public static void Main()
+        {
+            // Draw a mandelbrot set using a Canvas
+            var mandelbrot = Mandelbrot.Generate(32, 32);
+            Render(mandelbrot, "Mandelbrot");
+
+            // Draw an image using CanvasImage powered by ImageSharp.
+            // This requires the "Spectre.Console.ImageSharp" NuGet package.
+            var image = new CanvasImage("cake.png");
+            image.BilinearResampler();
+            image.MaxWidth(16);
+            Render(image, "Image from file (16 wide)");
+
+            // Draw image again, but without render width
+            image.NoMaxWidth();
+            image.Mutate(ctx => ctx.Grayscale().Rotate(-45).EntropyCrop());
+            Render(image, "Image from file (fit, greyscale, rotated)");
+        }
+
+        private static void Render(IRenderable canvas, string title)
+        {
+            AnsiConsole.WriteLine();
+            AnsiConsole.Render(new Rule($"[yellow]{title}[/]").LeftAligned().RuleStyle("grey"));
+            AnsiConsole.WriteLine();
+            AnsiConsole.Render(canvas);
+        }
+    }
+}