update HISTORY for 9.1

Author: rfindler

drracket/drracket/HISTORY.txt

@@ -2,6 +2,9 @@
        Version 9.1
 ------------------------------
 
+  . improve the handling of the dark mode preferences and improve the
+    GUI for choosing color schemes
+
   . improve the interactivity of on-paint when there are a lot of
     check-syntax arrows by caching the arrow drawing in a bitmap
     and computing the bitmap on multiple events
@@ -19,6 +22,11 @@
   . the contour window (via the menu-shortcut keystroke "u") shrinks
     when the widest line in the window got smaller
 
+  . improve the Insert Large Letters to be language-sensitive it the
+    choice of comment characters
+
+  . bug fixes and refactorings
+
 
 ------------------------------
        Version 9.0