ENH: Some documentation and add APPEND

Source/cmListCommand.cxx

@@ -38,7 +38,7 @@ bool cmListCommand::InitialPass(std::vector<std::string> const& args)
     {
     return this->HandleGetCommand(args);
     }
-  if(subCommand == "SET")
+  if(subCommand == "SET" || subCommand == "APPEND")
     {
     return this->HandleSetCommand(args);
     }

Source/cmListCommand.h

@@ -67,18 +67,21 @@ public:
       "  LIST(LENGTH <list> <output variable>)\n"
       "  LIST(GET <list> <element index> [<element index> ...] "
       "<output variable>)\n"
-      "  LIST(SET <list> <element> [<element> ...])\n"
+      "  LIST(APPEND <list> <element> [<element> ...])\n"
       "  LIST(INSERT <list> <element_index> <element> [<element> ...])\n"
-      "  LIST(REMOVE <variable> <value> [<value> ...])\n"
-      "  LIST(REMOVE_ITEM <variable> <index> [<index> ...])\n"
-      "  LIST(SORT <variable>)\n"
-      "  LIST(REVERSE <variable>)\n"
+      "  LIST(REMOVE <list> <value> [<value> ...])\n"
+      "  LIST(REMOVE_ITEM <list> <index> [<index> ...])\n"
+      "  LIST(SORT <list>)\n"
+      "  LIST(REVERSE <list>)\n"
       "LENGTH will return a given list's length.\n"
       "GET will return list of elements specified by indices from the list.\n"
-      "SET will append elements to the list.\n"
+      "APPEND will append elements to the list.\n"
       "INSERT will insert elements to the list to the specified location.\n"
       "When specifying an index, negative value corresponds to index from the"
       " end of the list.\n"
+      "REMOVE and REMOVE_ITEM will remove item from the list. The difference "
+      "is that REMOVE will remove the given items, while REMOVE_ITEM will "
+      "remove the item at the given indices.\n"
       ;
     }