Exclude testapp.c instead of internal_tests.c from docs.

Doxyfile

@@ -607,7 +607,7 @@ EXCLUDE_SYMLINKS       = NO
 # against the file with absolute path, so to exclude all test directories
 # for example use the pattern */test/*
 
-EXCLUDE_PATTERNS       = internal_tests.c
+EXCLUDE_PATTERNS       = testapp.c
 
 # The EXCLUDE_SYMBOLS tag can be used to specify one or more symbol names
 # (namespaces, classes, functions, etc.) that should be excluded from the