Update HISTORY.md

HISTORY.md

@@ -3,12 +3,19 @@
 ## in development:
 * **New Features:**
     * you can now also "peel off" custom block instances from their prototype templates in the block editor
+    * first-class colors, sorta, in the new "Colors" library, thanks, Brian!
 * **Notable Changes:**
     * speed-up  talk bubble positioning by 5x
 * **Notable Fixes:**
     * work around a floating point precision glitch in "ray length"
     * fixed an occasional rendering glitch when changing the display style of a variable watcher
     * fixed color effect for negative inputs, thanks, Brian!
+    * fixed some issues round bignums, thanks, Brian!
+* **Documentation Updates:**
+    * updated manual, thanks Brian!
+
+### 2021-05-03
+* new versions of "Colors" and bignums libraries, updated documentation, thanks, Brian
 
 ### 2021-04-23
 * objects: fixed color effect for negative inputs, thanks, Brian!