Update emoji support

* Add constants for emojis
* Move emoji shortcode rendering to Markup
* Add documentation
* Add example
* Add tests

src/Spectre.Console/Color.Generated.cs

@@ -1,7 +1,7 @@
 //------------------------------------------------------------------------------
 // <auto-generated>
 //     This code was generated by a tool.
-//     Generated 2020-08-03 15:17
+//     Generated 2020-09-18 10:42
 //
 //     Changes to this file may cause incorrect behavior and will be lost if
 //     the code is regenerated.

src/Spectre.Console/Emoji.cs

@@ -3,9 +3,9 @@ using System.Text.RegularExpressions;
 namespace Spectre.Console
 {
     /// <summary>
-    /// Utility class for working with emojis.
+    /// Utility for working with emojis.
     /// </summary>
-    internal static partial class Emoji
+    public static partial class Emoji
     {
         private static readonly Regex _emojiCode = new Regex(@"(:(\S*?):)", RegexOptions.Compiled);
 

src/Spectre.Console/Internal/Colors/ColorPalette.Generated.cs

@@ -1,7 +1,7 @@
 //------------------------------------------------------------------------------
 // <auto-generated>
 //     This code was generated by a tool.
-//     Generated 2020-08-03 15:17
+//     Generated 2020-09-18 10:42
 //
 //     Changes to this file may cause incorrect behavior and will be lost if
 //     the code is regenerated.

src/Spectre.Console/Internal/Colors/ColorTable.Generated.cs

@@ -1,7 +1,7 @@
 //------------------------------------------------------------------------------
 // <auto-generated>
 //     This code was generated by a tool.
-//     Generated 2020-08-03 15:17
+//     Generated 2020-09-18 10:42
 //
 //     Changes to this file may cause incorrect behavior and will be lost if
 //     the code is regenerated.

src/Spectre.Console/Internal/Text/Markup/MarkupParser.cs

@@ -8,6 +8,12 @@ namespace Spectre.Console.Internal
     {
         public static Paragraph Parse(string text, Style? style = null)
         {
+            if (text is null)
+            {
+                throw new ArgumentNullException(nameof(text));
+            }
+
+            text = Emoji.Replace(text);
             style ??= Style.Plain;
 
             var result = new Paragraph();

src/Spectre.Console/Rendering/Segment.cs

@@ -71,7 +71,7 @@ namespace Spectre.Console.Rendering
                 throw new ArgumentNullException(nameof(text));
             }
 
-            Text = Emoji.Replace(text).NormalizeLineEndings();
+            Text = text.NormalizeLineEndings();
             Style = style;
             IsLineBreak = lineBreak;
             IsWhiteSpace = string.IsNullOrWhiteSpace(text);