Merge pull request #267 from JordanMartinez/preventModelSubclass

Make StyledTextAreaModel package-private.

Author: TomasMikula

richtextfx/src/main/java/org/fxmisc/richtext/StyledTextAreaModel.java

@@ -33,7 +33,7 @@
  * @param <S> type of style that can be applied to text.
  * @param <PS> type of style that can be applied to Paragraph
  */
-public class StyledTextAreaModel<PS, S>
+class StyledTextAreaModel<PS, S>
         implements
         TextEditingArea<PS, S>,
         EditActions<PS, S>,