doc: extend "See Also" chapter rendering for ff* tools

Add more references, and generate alternative variants for HTML and POD
output. In particular, this allows to render a "See Also" chapter in the
HTML output.

doc/ffmpeg.texi

@@ -1289,6 +1289,28 @@ ffmpeg -i src.ext -lmax 21*QP2LAMBDA dst.ext
 @include filters.texi
 @include metadata.texi
 
+@chapter See Also
+
+@ifhtml
+@url{ffplay.html,ffplay}, @url{ffprobe.html,ffprobe}, @url{ffserver.html,ffserver},
+@url{ffmpeg-utils.html,ffmpeg-utils},
+@url{ffmpeg-scaler.html,ffmpeg-scaler},
+@url{ffmpeg-resampler.html,ffmpeg-resampler},
+@url{ffmpeg-codecs.html,ffmpeg-codecs},
+@url{ffmpeg-bitstream-filters,ffmpeg-bitstream-filters},
+@url{ffmpeg-formats.html,ffmpeg-formats},
+@url{ffmpeg-devices.html,ffmpeg-devices},
+@url{ffmpeg-protocols.html,ffmpeg-protocols},
+@url{ffmpeg-filters.html,ffmpeg-filters}
+@end ifhtml
+
+@ifnothtml
+ffplay(1), ffprobe(1), ffserver(1),
+ffmpeg-utils(1), ffmpeg-scaler(1), ffmpeg-resampler(1),
+ffmpeg-codecs(1), ffmpeg-bitstream-filters(1), ffmpeg-formats(1),
+ffmpeg-devices(1), ffmpeg-protocols(1), ffmpeg-filters(1)
+@end ifnothtml
+
 @include authors.texi
 
 @ignore
@@ -1296,10 +1318,6 @@ ffmpeg -i src.ext -lmax 21*QP2LAMBDA dst.ext
 @setfilename ffmpeg
 @settitle ffmpeg video converter
 
-@c man begin SEEALSO
-ffplay(1), ffprobe(1), ffserver(1) and the FFmpeg HTML documentation
-@c man end
-
 @end ignore
 
 @bye

doc/ffplay.texi

@@ -196,6 +196,28 @@ Seek to percentage in file corresponding to fraction of width.
 @include protocols.texi
 @include filters.texi
 
+@chapter See Also
+
+@ifhtml
+@url{ffmpeg.html,ffmpeg}, @url{ffprobe.html,ffprobe}, @url{ffserver.html,ffserver},
+@url{ffmpeg-utils.html,ffmpeg-utils},
+@url{ffmpeg-scaler.html,ffmpeg-scaler},
+@url{ffmpeg-resampler.html,ffmpeg-resampler},
+@url{ffmpeg-codecs.html,ffmpeg-codecs},
+@url{ffmpeg-bitstream-filters,ffmpeg-bitstream-filters},
+@url{ffmpeg-formats.html,ffmpeg-formats},
+@url{ffmpeg-devices.html,ffmpeg-devices},
+@url{ffmpeg-protocols.html,ffmpeg-protocols},
+@url{ffmpeg-filters.html,ffmpeg-filters}
+@end ifhtml
+
+@ifnothtml
+ffmpeg(1), ffprobe(1), ffserver(1),
+ffmpeg-utils(1), ffmpeg-scaler(1), ffmpeg-resampler(1),
+ffmpeg-codecs(1), ffmpeg-bitstream-filters(1), ffmpeg-formats(1),
+ffmpeg-devices(1), ffmpeg-protocols(1), ffmpeg-filters(1)
+@end ifnothtml
+
 @include authors.texi
 
 @ignore
@@ -203,10 +225,6 @@ Seek to percentage in file corresponding to fraction of width.
 @setfilename ffplay
 @settitle FFplay media player
 
-@c man begin SEEALSO
-ffmpeg(1), ffprobe(1), ffserver(1) and the FFmpeg HTML documentation
-@c man end
-
 @end ignore
 
 @bye

doc/ffprobe.texi

@@ -493,6 +493,28 @@ DV, GXF and AVI timecodes are available in format metadata
 @include protocols.texi
 @include indevs.texi
 
+@chapter See Also
+
+@ifhtml
+@url{ffplay.html,ffmpeg}, @url{ffprobe.html,ffprobe}, @url{ffserver.html,ffserver},
+@url{ffmpeg-utils.html,ffmpeg-utils},
+@url{ffmpeg-scaler.html,ffmpeg-scaler},
+@url{ffmpeg-resampler.html,ffmpeg-resampler},
+@url{ffmpeg-codecs.html,ffmpeg-codecs},
+@url{ffmpeg-bitstream-filters,ffmpeg-bitstream-filters},
+@url{ffmpeg-formats.html,ffmpeg-formats},
+@url{ffmpeg-devices.html,ffmpeg-devices},
+@url{ffmpeg-protocols.html,ffmpeg-protocols},
+@url{ffmpeg-filters.html,ffmpeg-filters}
+@end ifhtml
+
+@ifnothtml
+ffmpeg(1), ffplay(1), ffserver(1),
+ffmpeg-utils(1), ffmpeg-scaler(1), ffmpeg-resampler(1),
+ffmpeg-codecs(1), ffmpeg-bitstream-filters(1), ffmpeg-formats(1),
+ffmpeg-devices(1), ffmpeg-protocols(1), ffmpeg-filters(1)
+@end ifnothtml
+
 @include authors.texi
 
 @ignore
@@ -500,10 +522,6 @@ DV, GXF and AVI timecodes are available in format metadata
 @setfilename ffprobe
 @settitle ffprobe media prober
 
-@c man begin SEEALSO
-ffmpeg(1), ffplay(1), ffserver(1) and the FFmpeg HTML documentation
-@c man end
-
 @end ignore
 
 @bye

doc/ffserver.texi

@@ -260,6 +260,29 @@ messages to stdout.
 @end table
 @c man end
 
+@chapter See Also
+
+@ifhtml
+The @file{doc/ffserver.conf} example,
+@url{ffmpeg.html,ffmpeg}, @url{ffplay.html,ffplay}, @url{ffprobe.html,ffprobe},
+@url{ffmpeg-utils.html,ffmpeg-utils},
+@url{ffmpeg-scaler.html,ffmpeg-scaler},
+@url{ffmpeg-resampler.html,ffmpeg-resampler},
+@url{ffmpeg-codecs.html,ffmpeg-codecs},
+@url{ffmpeg-bitstream-filters,ffmpeg-bitstream-filters},
+@url{ffmpeg-formats.html,ffmpeg-formats},
+@url{ffmpeg-devices.html,ffmpeg-devices},
+@url{ffmpeg-protocols.html,ffmpeg-protocols},
+@url{ffmpeg-filters.html,ffmpeg-filters}
+@end ifhtml
+
+@ifnothtml
+The @file{doc/ffserver.conf} example, ffmpeg(1), ffplay(1), ffprobe(1),
+ffmpeg-utils(1), ffmpeg-scaler(1), ffmpeg-resampler(1),
+ffmpeg-codecs(1), ffmpeg-bitstream-filters(1), ffmpeg-formats(1),
+ffmpeg-devices(1), ffmpeg-protocols(1), ffmpeg-filters(1)
+@end ifnothtml
+
 @include authors.texi
 
 @ignore
@@ -267,12 +290,6 @@ messages to stdout.
 @setfilename ffserver
 @settitle ffserver video server
 
-@c man begin SEEALSO
-
-ffmpeg(1), ffplay(1), ffprobe(1), the @file{ffserver.conf}
-example and the FFmpeg HTML documentation
-@c man end
-
 @end ignore
 
 @bye