doc: extend "See Also" chapters in library manuals

In particular, make "See Also" chapter rendered in HTML output.

doc/libavcodec.texi

@@ -22,6 +22,20 @@ implementing robust and fast codecs as well as for experimentation.
 
 @c man end DESCRIPTION
 
+@chapter See Also
+
+@ifhtml
+@url{ffmpeg.html,ffmpeg}, @url{ffplay.html,ffplay}, @url{ffprobe.html,ffprobe}, @url{ffserver.html,ffserver},
+@url{ffmpeg-codecs.html,ffmpeg-codecs}, @url{ffmpeg-bitstream-filters.html,bitstream-filters},
+@url{libavutil.html,libavutil}
+@end ifhtml
+
+@ifnothtml
+ffmpeg(1), ffplay(1), ffprobe(1), ffserver(1),
+ffmpeg-codecs(1), ffmpeg-bitstream-filters(1),
+libavutil(3)
+@end ifnothtml
+
 @include authors.texi
 
 @ignore
@@ -29,11 +43,6 @@ implementing robust and fast codecs as well as for experimentation.
 @setfilename libavcodec
 @settitle media streams decoding and encoding library
 
-@c man begin SEEALSO
-ffmpeg(1), ffplay(1), ffprobe(1), ffserver(1), ffmpeg-codecs(1),
-ffmpeg-bitstream-filters(1), libavutil(3)
-@c man end
-
 @end ignore
 
 @bye

doc/libavdevice.texi

@@ -19,6 +19,20 @@ VfW, DShow, and ALSA.
 
 @c man end DESCRIPTION
 
+@chapter See Also
+
+@ifhtml
+@url{ffmpeg.html,ffmpeg}, @url{ffplay.html,ffplay}, @url{ffprobe.html,ffprobe}, @url{ffserver.html,ffserver},
+@url{ffmpeg-devices.html,ffmpeg-devices},
+@url{libavutil.html,libavutil}, @url{libavcodec.html,libavcodec}, @url{libavformat.html,libavformat}
+@end ifhtml
+
+@ifnothtml
+ffmpeg(1), ffplay(1), ffprobe(1), ffserver(1),
+ffmpeg-devices(1),
+libavutil(3), libavcodec(3), libavformat(3)
+@end ifnothtml
+
 @include authors.texi
 
 @ignore
@@ -26,11 +40,6 @@ VfW, DShow, and ALSA.
 @setfilename libavdevice
 @settitle multimedia device handling library
 
-@c man begin SEEALSO
-ffmpeg(1), ffplay(1), ffprobe(1), ffserver(1), libavutil(3),
-libavcodec(3), libavformat(3), ffmpeg-devices(1)
-@c man end
-
 @end ignore
 
 @bye

doc/libavfilter.texi

@@ -17,6 +17,21 @@ framework containing several filters, sources and sinks.
 
 @c man end DESCRIPTION
 
+@chapter See Also
+
+@ifhtml
+@url{ffmpeg.html,ffmpeg}, @url{ffplay.html,ffplay}, @url{ffprobe.html,ffprobe}, @url{ffserver.html,ffserver},
+@url{ffmpeg-filters.html,ffmpeg-filters},
+@url{libavutil.html,libavutil}, @url{libswscale.html,libswscale}, @url{libswresample.html,libswresample},
+@url{libavcodec.html,libavcodec}, @url{libavformat.html,libavformat}, @url{libavdevice.html,libavdevice}
+@end ifhtml
+
+@ifnothtml
+ffmpeg(1), ffplay(1), ffprobe(1), ffserver(1),
+ffmpeg-filters(1),
+libavutil(3), libswscale(3), libswresample(3), libavcodec(3), libavformat(3), libavdevice(3)
+@end ifnothtml
+
 @include authors.texi
 
 @ignore
@@ -24,10 +39,6 @@ framework containing several filters, sources and sinks.
 @setfilename libavfilter
 @settitle multimedia filtering library
 
-@c man begin SEEALSO
-ffmpeg(1), ffplay(1), ffprobe(1), ffserver(1), ffmpeg-filters(1)
-@c man end
-
 @end ignore
 
 @bye

doc/libavformat.texi

@@ -22,6 +22,20 @@ resource.
 
 @c man end DESCRIPTION
 
+@chapter See Also
+
+@ifhtml
+@url{ffmpeg.html,ffmpeg}, @url{ffplay.html,ffplay}, @url{ffprobe.html,ffprobe}, @url{ffserver.html,ffserver},
+@url{ffmpeg-formats.html,ffmpeg-formats}, @url{ffmpeg-protocols.html,ffmpeg-protocols},
+@url{libavutil.html,libavutil}, @url{libavcodec.html,libavcodec}
+@end ifhtml
+
+@ifnothtml
+ffmpeg(1), ffplay(1), ffprobe(1), ffserver(1),
+ffmpeg-formats(1), ffmpeg-protocols(1),
+libavutil(3), libavcodec(3)
+@end ifnothtml
+
 @include authors.texi
 
 @ignore
@@ -29,10 +43,6 @@ resource.
 @setfilename libavformat
 @settitle multimedia muxing and demuxing library
 
-@c man begin SEEALSO
-ffmpeg(1), ffplay(1), ffprobe(1), ffserver(1), libavutil(3), libavcodec(3), ffmpeg-formats(1), ffmpeg-protocols(1)
-@c man end
-
 @end ignore
 
 @bye

doc/libavutil.texi

@@ -20,6 +20,18 @@ enumerations for pixel and sample formats).
 
 @c man end DESCRIPTION
 
+@chapter See Also
+
+@ifhtml
+@url{ffmpeg.html,ffmpeg}, @url{ffplay.html,ffplay}, @url{ffprobe.html,ffprobe}, @url{ffserver.html,ffserver},
+@url{ffmpeg-utils.html,ffmpeg-utils}
+@end ifhtml
+
+@ifnothtml
+ffmpeg(1), ffplay(1), ffprobe(1), ffserver(1),
+ffmpeg-utils(1)
+@end ifnothtml
+
 @include authors.texi
 
 @ignore
@@ -27,10 +39,6 @@ enumerations for pixel and sample formats).
 @setfilename libavutil
 @settitle multimedia-biased utility library
 
-@c man begin SEEALSO
-ffmpeg(1), ffplay(1), ffprobe(1), ffserver(1), ffmpeg-utils(1)
-@c man end
-
 @end ignore
 
 @bye

doc/libswresample.texi

@@ -44,6 +44,20 @@ enabled through dedicated options.
 
 @c man end DESCRIPTION
 
+@chapter See Also
+
+@ifhtml
+@url{ffmpeg.html,ffmpeg}, @url{ffplay.html,ffplay}, @url{ffprobe.html,ffprobe}, @url{ffserver.html,ffserver},
+@url{ffmpeg-resampler.html,ffmpeg-resampler},
+@url{libavutil.html,libavutil}
+@end ifhtml
+
+@ifnothtml
+ffmpeg(1), ffplay(1), ffprobe(1), ffserver(1),
+ffmpeg-resampler(1),
+libavutil(3)
+@end ifnothtml
+
 @include authors.texi
 
 @ignore
@@ -51,10 +65,6 @@ enabled through dedicated options.
 @setfilename libswresample
 @settitle audio resampling library
 
-@c man begin SEEALSO
-ffmpeg(1), ffplay(1), ffprobe(1), ffserver(1), ffmpeg-resampler(1), libavutil(3)
-@c man end
-
 @end ignore
 
 @bye

doc/libswscale.texi

@@ -37,6 +37,20 @@ colorspaces differ.
 
 @c man end DESCRIPTION
 
+@chapter See Also
+
+@ifhtml
+@url{ffmpeg.html,ffmpeg}, @url{ffplay.html,ffplay}, @url{ffprobe.html,ffprobe}, @url{ffserver.html,ffserver},
+@url{ffmpeg-scaler.html,ffmpeg-scaler},
+@url{libavutil.html,libavutil}
+@end ifhtml
+
+@ifnothtml
+ffmpeg(1), ffplay(1), ffprobe(1), ffserver(1),
+ffmpeg-scaler(1),
+libavutil(3)
+@end ifnothtml
+
 @include authors.texi
 
 @ignore
@@ -44,10 +58,6 @@ colorspaces differ.
 @setfilename libswscale
 @settitle video scaling and pixel format conversion library
 
-@c man begin SEEALSO
-ffmpeg(1), ffplay(1), ffprobe(1), ffserver(1), ffmpeg-scaler(1), libavutil(3)
-@c man end
-
 @end ignore
 
 @bye