doc/examples/Makefile: split lines up to make diffs that change them clearer

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

doc/examples/Makefile

 # use pkg-config for getting CFLAGS abd LDFLAGS
-FFMPEG_LIBS=libavdevice libavformat libavfilter libavcodec libswscale libavutil
+FFMPEG_LIBS=    libavdevice                        \
+                libavformat                        \
+                libavfilter                        \
+                libavcodec                         \
+                libswscale                         \
+                libavutil                          \
+
 CFLAGS+=-Wall $(shell pkg-config  --cflags $(FFMPEG_LIBS))
 LDFLAGS+=$(shell pkg-config --libs $(FFMPEG_LIBS))
 
-EXAMPLES=decoding_encoding filtering_video filtering_audio metadata muxing
+EXAMPLES=       decoding_encoding                  \
+                filtering_video                    \
+                filtering_audio                    \
+                metadata                           \
+                muxing                             \
 
 OBJS=$(addsuffix .o,$(EXAMPLES))