Added initial support for rendering composites

This is far from complete, but it's a start
and it will enable us to create things like tables
and other complex objects in the long run.

src/Spectre.Console/Capabilities.cs

@@ -0,0 +1,42 @@
+namespace Spectre.Console
+{
+    /// <summary>
+    /// Represents console capabilities.
+    /// </summary>
+    public sealed class Capabilities
+    {
+        /// <summary>
+        /// Gets a value indicating whether or not
+        /// the console supports Ansi.
+        /// </summary>
+        public bool SupportsAnsi { get; }
+
+        /// <summary>
+        /// Gets the color system.
+        /// </summary>
+        public ColorSystem ColorSystem { get; }
+
+        internal Capabilities(bool supportsAnsi, ColorSystem colorSystem)
+        {
+            SupportsAnsi = supportsAnsi;
+            ColorSystem = colorSystem;
+        }
+
+        /// <inheritdoc/>
+        public override string ToString()
+        {
+            var supportsAnsi = SupportsAnsi ? "Yes" : "No";
+            var bits = ColorSystem switch
+            {
+                ColorSystem.NoColors => "1 bit",
+                ColorSystem.Legacy => "3 bits",
+                ColorSystem.Standard => "4 bits",
+                ColorSystem.EightBit => "8 bits",
+                ColorSystem.TrueColor => "24 bits",
+                _ => "?"
+            };
+
+            return $"ANSI={supportsAnsi}, Colors={ColorSystem} ({bits})";
+        }
+    }
+}