examples: move API examples to a dedicated dir in doc

doc/examples/Makefile

+# use pkg-config for getting CFLAGS abd LDFLAGS
+FFMPEG_LIBS=libavdevice libavformat libavfilter libavcodec libswscale libavutil
+CFLAGS+=$(shell pkg-config  --cflags $(FFMPEG_LIBS))
+LDFLAGS+=$(shell pkg-config --libs $(FFMPEG_LIBS))
+
+EXAMPLES=api-example output-example
+
+OBJS=$(addsuffix .o,$(EXAMPLES))
+
+%: %.o
+	$(CC) $< $(LDFLAGS) -o $@
+
+%.o: %.c
+	$(CC) $< $(CFLAGS) -c -o $@
+
+.phony: all clean
+
+all: $(OBJS) $(EXAMPLES)
+
+clean:
+	rm -rf $(EXAMPLES) $(OBJS)

libavcodec/Makefile

@@ -674,8 +674,6 @@ SKIPHEADERS-$(CONFIG_VAAPI)            += vaapi_internal.h
 SKIPHEADERS-$(CONFIG_VDPAU)            += vdpau.h
 SKIPHEADERS-$(CONFIG_XVMC)             += xvmc.h
 
-EXAMPLES = api
-
 TESTPROGS = cabac dct eval fft fft-fixed h264 iirfilter rangecoder snow
 TESTPROGS-$(HAVE_MMX) += motion
 TESTOBJS = dctref.o

libavformat/Makefile

@@ -340,7 +340,6 @@ OBJS-$(CONFIG_UDP_PROTOCOL)              += udp.o
 # libavdevice dependencies
 OBJS-$(CONFIG_JACK_INDEV)                += timefilter.o
 
-EXAMPLES  = output
 TESTPROGS = timefilter
 
 include $(SUBDIR)../subdir.mak