examples: fix doxy so they appear on the example page

Signed-off-by: Michael Niedermayer <michaelni@gmx.at>

doc/examples/decoding_encoding.c

@@ -27,6 +27,7 @@
  * Note that libavcodec only handles codecs (mpeg, mpeg4, etc...),
  * not file formats (avi, vob, mp4, mov, mkv, mxf, flv, mpegts, mpegps, etc...). See library 'libavformat' for the
  * format handling
+ * @example doc/examples/decoding_encoding.c
  */
 
 #include <math.h>

doc/examples/demuxing.c

@@ -26,6 +26,7 @@
  *
  * Show how to use the libavformat and libavcodec API to demux and
  * decode audio and video data.
+ * @example doc/examples/demuxing.c
  */
 
 #include <libavutil/imgutils.h>

doc/examples/filtering_audio.c

@@ -25,6 +25,7 @@
 /**
  * @file
  * API example for audio decoding and filtering
+ * @example doc/examples/filtering_audio.c
  */
 
 #include <unistd.h>

doc/examples/filtering_video.c

@@ -24,6 +24,7 @@
 /**
  * @file
  * API example for decoding and filtering
+ * @example doc/examples/filtering_video.c
  */
 
 #define _XOPEN_SOURCE 600 /* for usleep */

doc/examples/metadata.c

@@ -23,6 +23,7 @@
 /**
  * @file
  * Shows how the metadata API can be used in application programs.
+ * @example doc/examples/metadata.c
  */
 
 #include <stdio.h>

doc/examples/muxing.c

@@ -26,6 +26,7 @@
  *
  * Output a media file in any supported libavformat format.
  * The default codecs are used.
+ * @example doc/examples/muxing.c
  */
 
 #include <stdlib.h>

doc/examples/scaling_video.c

@@ -23,6 +23,7 @@
 /**
  * @file
  * libswscale API use example.
+ * @example doc/examples/scaling_video.c
  */
 
 #include <libavutil/imgutils.h>