Make RichTextWriter and derived classes internal; they're not necessary for using RichText/RichTextModel anymore.

If no new usecase comes up, these classes can be deleted (except maybe for HtmlRichTextWriter).

src/Libraries/AvalonEdit/ICSharpCode.AvalonEdit/Highlighting/HighlightedLine.cs

@@ -205,7 +205,7 @@ namespace ICSharpCode.AvalonEdit.Highlighting
 		/// <summary>
 		/// Writes the highlighted line to the RichTextWriter.
 		/// </summary>
-		public void WriteTo(RichTextWriter writer)
+		internal void WriteTo(RichTextWriter writer)
 		{
 			int startOffset = this.DocumentLine.Offset;
 			WriteTo(writer, startOffset, startOffset + this.DocumentLine.Length);
@@ -214,7 +214,7 @@ namespace ICSharpCode.AvalonEdit.Highlighting
 		/// <summary>
 		/// Writes a part of the highlighted line to the RichTextWriter.
 		/// </summary>
-		public void WriteTo(RichTextWriter writer, int startOffset, int endOffset)
+		internal void WriteTo(RichTextWriter writer, int startOffset, int endOffset)
 		{
 			if (writer == null)
 				throw new ArgumentNullException("writer");

src/Libraries/AvalonEdit/ICSharpCode.AvalonEdit/Highlighting/HtmlRichTextWriter.cs

@@ -15,7 +15,7 @@ namespace ICSharpCode.AvalonEdit.Highlighting
 	/// <summary>
 	/// RichTextWriter implementation that produces HTML.
 	/// </summary>
-	public class HtmlRichTextWriter : RichTextWriter
+	class HtmlRichTextWriter : RichTextWriter
 	{
 		readonly TextWriter htmlWriter;
 		readonly HtmlOptions options;

src/Libraries/AvalonEdit/ICSharpCode.AvalonEdit/Highlighting/RichTextModelWriter.cs

@@ -14,9 +14,9 @@ using ICSharpCode.AvalonEdit.Utils;
 namespace ICSharpCode.AvalonEdit.Highlighting
 {
 	/// <summary>
-	/// A RichTextWriter that writes into a document and .
+	/// A RichTextWriter that writes into a document and RichTextModel.
 	/// </summary>
-	public class RichTextModelWriter : PlainRichTextWriter
+	class RichTextModelWriter : PlainRichTextWriter
 	{
 		readonly RichTextModel richTextModel;
 		readonly DocumentTextWriter documentTextWriter;

src/Libraries/AvalonEdit/ICSharpCode.AvalonEdit/Utils/PlainRichTextWriter.cs

@@ -11,7 +11,7 @@ namespace ICSharpCode.AvalonEdit.Utils
 	/// RichTextWriter implementation that writes plain text only
 	/// and ignores all formatted spans.
 	/// </summary>
-	public class PlainRichTextWriter : RichTextWriter
+	class PlainRichTextWriter : RichTextWriter
 	{
 		/// <summary>
 		/// The text writer that was passed to the PlainRichTextWriter constructor.

src/Libraries/AvalonEdit/ICSharpCode.AvalonEdit/Utils/RichTextWriter.cs

@@ -12,7 +12,7 @@ namespace ICSharpCode.AvalonEdit.Utils
 	/// <summary>
 	/// A text writer that supports creating spans of highlighted text.
 	/// </summary>
-	public abstract class RichTextWriter : TextWriter
+	abstract class RichTextWriter : TextWriter
 	{
 		/// <summary>
 		/// Gets called by the RichTextWriter base class when a BeginSpan() method