assign ID 0028 and rename accordingly

Author: book

ppcs/ppcTODO-custom-prefix-postfix-operators.md renamed to ppcs/ppc0028-custom-prefix-postfix-operators.md

@@ -4,7 +4,7 @@
 
     Author:  Paul Evans <PEVANS>
     Sponsor:
-    ID:      TODO
+    ID:      0028
     Status:  Exploratory
 
 ## Abstract