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.Tests/Extensions/StringExtensions.cs

@@ -0,0 +1,13 @@
+using System;
+
+namespace Spectre.Console.Tests
+{
+    public static class StringExtensions
+    {
+        public static string NormalizeLineEndings(this string text)
+        {
+            return text?.Replace("\r\n", "\n", StringComparison.OrdinalIgnoreCase)
+                ?.Replace("\r", string.Empty, StringComparison.OrdinalIgnoreCase);
+        }
+    }
+}