doc/examples: add programs to .gitignore.

.gitignore

@@ -33,6 +33,11 @@ avconv
 doc/avoptions_codec.texi
 doc/avoptions_format.texi
 doc/print_options
+doc/examples/decoding_encoding
+doc/examples/filtering_audio
+doc/examples/filtering_video
+doc/examples/metadata
+doc/examples/muxing
 libavcodec/*_tablegen
 libavcodec/*_tables.c
 libavcodec/*_tables.h