Update CHANGES and UPGRADE.txt for certified/16.8-cert4

CHANGES

@@ -12,6 +12,28 @@
 ===
 ==============================================================================
 
+------------------------------------------------------------------------------
+--- Functionality changes from Asterisk certified/16.8-cert3 to Asterisk certified/16.8-cert4 
+------------------------------------------------------------------------------
+
+AMI
+------------------
+ * You can now specify an optional 'Content-Type' as an argument for the Asterisk
+   SendText manager action.
+
+logger
+------------------
+ * Added a new log formatter called "plain" that always prints
+   file, function and line number if available (even for verbose
+   messages) and never prints color control characters.  Most
+   suitable for file output but can be used for other channels
+   as well.
+
+   You use it in logger.conf like so:
+   debug => [plain]debug
+   console => [plain]error,warning,debug,notice,pjsip_history
+   messages => [plain]warning,error,verbose
+
 ------------------------------------------------------------------------------
 --- Functionality changes from Asterisk certified/16.8-cert1-rc3 to Asterisk certified/16.8-cert1-rc4 
 ------------------------------------------------------------------------------

doc/CHANGES-staging/ami_sendtext_content_type.txt

@@ -1,4 +0,0 @@
-Subject: AMI
-
-You can now specify an optional 'Content-Type' as an argument for the Asterisk
-SendText manager action.

doc/CHANGES-staging/logger_format.txt

@@ -1,12 +0,0 @@
-Subject: logger
-
-Added a new log formatter called "plain" that always prints
-file, function and line number if available (even for verbose
-messages) and never prints color control characters.  Most
-suitable for file output but can be used for other channels
-as well.
-
-You use it in logger.conf like so:
-debug => [plain]debug
-console => [plain]error,warning,debug,notice,pjsip_history
-messages => [plain]warning,error,verbose