Implement Rewind across tracks functionality

Useful feature for audiobooks. To rewind from the end of the previous track - press rewind at the very beginning of the current track. So if you are in the middle of the track - first rewind till beginning then release and press rewind button again (Playback Settings -> Rewind Across Tracks option should be enabled)

Fixes FS#13290

Change-Id: I5d7f06f64ad76d1e8f7827fe594ccca5f621769d

manual/appendix/config_file_options.tex

@@ -174,6 +174,8 @@
             90s, 2min, 3min, 5min, 10min, 15min & N/A\\
     prevent track skip
                     & on, off           & N/A\\
+    rewind across tracks
+                    & on, off           & N/A\\
     start in screen & previous, root, files, dB, wps, menu,
       \opt{recording}{recording, }
       \opt{radio}{radio, }

manual/configure_rockbox/playback_options.tex

@@ -287,6 +287,11 @@ you to configure settings related to audio playback.
   if a track ends, which can be achieved by combining this option with
   \setting{Repeat} set to \setting{One}
 
+\section{Rewind Across Tracks}\index{Rewind Across Tracks}
+  Enables rewinding to the end of the previous track. When enabled pressing rewind
+  at the very beginning of the current track (first 3 seconds) skips to the end of
+  the previous track.
+
 \section{Rewind Before Resume}\index{Rewind Before Resume}
   When restarting a track or a bookmark, a short rewind can be done before the
   playback is started. This can be useful when listening to speech material,