Add setting for numeric list sort order

The sort order of numeric lists can now be changed with the
new "List Order" setting. It defaults to ascending for most
scrollwheel targets and descending for all others, matching
the old hardcoded behavior.

Change-Id: I4866f04ec5995158edf9e40badf7f661b3ddea81

manual/appendix/config_file_options.tex

@@ -65,6 +65,7 @@
     bidir limit     & 0 to 200          & \% screen\\
     scroll paginated & on, off & N/A\\
     list wraparound & on, off & N/A\\
+    list order      & ascending, descending & N/A\\
     hold\_lr\_for\_scroll\_in\_list & on, off & N/A\\
     show path in browser & off, current directory, full path & N/A\\
     contrast        & 0 to 63           & N/A\\

manual/configure_rockbox/display_options.tex

@@ -210,6 +210,12 @@
     \item[List Wraparound.]
       When set to \setting{Yes}, scrolling will wrap around back to the opposite
       end of a list after the first or last item has been reached.
+    \item[List Order.]
+      When set to \setting{Ascending}, numeric lists such as brightness and
+      volume will be sorted with the smallest value at the top of the list and
+      values increasing down the list. When set to \setting{Descending}, the
+      order is reversed -- the largest value is sorted at the top and values
+      will decrease down the list.
     \nopt{scrollwheel}{
       \item[List Acceleration Start Delay.]
         This setting enables the acceleration of scroll speed in lists when