doxygen: be more permissive when searching for API examples

(cherry picked from commit 7655cfb1b8)

Doxyfile

@@ -591,14 +591,14 @@ EXCLUDE_SYMBOLS        =
 # directories that contain example code fragments that are included (see
 # the \include command).
 
-EXAMPLE_PATH           =
+EXAMPLE_PATH           = libavcodec/ libavformat/
 
 # If the value of the EXAMPLE_PATH tag contains directories, you can use the
 # EXAMPLE_PATTERNS tag to specify one or more wildcard pattern (like *.cpp
 # and *.h) to filter out the source-files in the directories. If left
 # blank all files are included.
 
-EXAMPLE_PATTERNS       =
+EXAMPLE_PATTERNS       = *-example.c
 
 # If the EXAMPLE_RECURSIVE tag is set to YES then subdirectories will be
 # searched for input files to be used with the \include or \dontinclude