release version 9.0

Problem:    About time to release Vim 9.0.
Solution:   Update the version number everywhere.
diff --git a/runtime/doc/howto.txt b/runtime/doc/howto.txt
index 1b10025..75169a9 100644
--- a/runtime/doc/howto.txt
+++ b/runtime/doc/howto.txt
@@ -1,4 +1,4 @@
-*howto.txt*	For Vim version 8.2.  Last change: 2006 Apr 02
+*howto.txt*	For Vim version 9.0.  Last change: 2006 Apr 02
 
 
 		  VIM REFERENCE MANUAL	  by Bram Moolenaar