doc/examples: use system headers in decoding_encoding and muxing.

All the other examples already use the system installed headers.

doc/examples/decoding_encoding.c

@@ -31,11 +31,11 @@
 
 #include <math.h>
 
-#include "libavutil/imgutils.h"
-#include "libavutil/opt.h"
-#include "libavcodec/avcodec.h"
-#include "libavutil/mathematics.h"
-#include "libavutil/samplefmt.h"
+#include <libavutil/imgutils.h>
+#include <libavutil/opt.h>
+#include <libavcodec/avcodec.h>
+#include <libavutil/mathematics.h>
+#include <libavutil/samplefmt.h>
 
 #define INBUF_SIZE 4096
 #define AUDIO_INBUF_SIZE 20480

doc/examples/muxing.c

@@ -33,9 +33,9 @@
 #include <string.h>
 #include <math.h>
 
-#include "libavutil/mathematics.h"
-#include "libavformat/avformat.h"
-#include "libswscale/swscale.h"
+#include <libavutil/mathematics.h>
+#include <libavformat/avformat.h>
+#include <libswscale/swscale.h>
 
 #undef exit