Add Scaletempo audio filter

Scaletempo maintains the audio pitch when playback rate != 1.0 (i.e.
no chipmunk effect).  This fixes the pitch scaling caused by using the
resampler to handle playback rate.

Ported from GStreamer.  Inspired by SoundTouch library by Olli Parviainen.
Signed-off-by: Rémi Denis-Courmont <rdenis@simphalempin.com>

configure.ac

@@ -1216,6 +1216,7 @@ if test "${SYS}" != "mingwce"; then
   VLC_ADD_PLUGIN([normvol])
   VLC_ADD_PLUGIN([equalizer])
   VLC_ADD_PLUGIN([param_eq])
+  VLC_ADD_PLUGIN([scaletempo])
   VLC_ADD_PLUGIN([converter_float])
   VLC_ADD_PLUGIN([a52tospdif])
   VLC_ADD_PLUGIN([dtstospdif])

modules/audio_filter/Modules.am

@@ -3,3 +3,4 @@ SOURCES_equalizer = equalizer.c equalizer_presets.h
 SOURCES_normvol = normvol.c
 SOURCES_audio_format = format.c
 SOURCES_param_eq = param_eq.c
+SOURCES_scaletempo = scaletempo.c