Improve text composite

- A `Text` object should not be able to justify itself.
  All justification needs to be done by a parent.
- Apply colors and styles to part of a `Text` object
- Markup parser should return a `Text` object

src/Spectre.Console/Internal/Extensions/AppearanceExtensions.cs

@@ -0,0 +1,18 @@
+using System.Collections.Generic;
+
+namespace Spectre.Console.Internal
+{
+    internal static class AppearanceExtensions
+    {
+        public static Appearance Combine(this Appearance appearance, IEnumerable<Appearance> source)
+        {
+            var current = appearance;
+            foreach (var item in source)
+            {
+                current = current.Combine(item);
+            }
+
+            return current;
+        }
+    }
+}

src/Spectre.Console/Internal/Extensions/CharExtensions.cs

@@ -1,12 +0,0 @@
-using System.Text;
-
-namespace Spectre.Console.Internal
-{
-    internal static class CharExtensions
-    {
-        public static int CellLength(this char token, Encoding encoding)
-        {
-            return Cell.GetCellLength(encoding, token);
-        }
-    }
-}

src/Spectre.Console/Internal/Extensions/ConsoleExtensions.cs

@@ -1,6 +1,5 @@
 using System;
 using System.Diagnostics.CodeAnalysis;
-using Spectre.Console.Composition;
 
 namespace Spectre.Console.Internal
 {

src/Spectre.Console/Internal/Extensions/EnumerableExtensions.cs

@@ -0,0 +1,44 @@
+using System;
+using System.Collections.Generic;
+using System.Linq;
+
+namespace Spectre.Console.Internal
+{
+    internal static class EnumerableExtensions
+    {
+        public static IEnumerable<(int Index, bool First, bool Last, T Item)> Enumerate<T>(this IEnumerable<T> source)
+        {
+            if (source is null)
+            {
+                throw new ArgumentNullException(nameof(source));
+            }
+
+            return Enumerate(source.GetEnumerator());
+        }
+
+        public static IEnumerable<(int Index, bool First, bool Last, T Item)> Enumerate<T>(this IEnumerator<T> source)
+        {
+            if (source is null)
+            {
+                throw new ArgumentNullException(nameof(source));
+            }
+
+            var first = true;
+            var last = !source.MoveNext();
+            T current;
+
+            for (var index = 0; !last; index++)
+            {
+                current = source.Current;
+                last = !source.MoveNext();
+                yield return (index, first, last, current);
+                first = false;
+            }
+        }
+
+        public static IEnumerable<TResult> SelectIndex<T, TResult>(this IEnumerable<T> source, Func<T, int, TResult> func)
+        {
+            return source.Select((value, index) => func(value, index));
+        }
+    }
+}