Lists all the files contained within the given parent directory.
| directory | 
                 the GLib.File parent directory  | 
            
| include_subdirs | 
                 whether or not to include files found within sub-directories  | 
            
| cancellable | 
                 the optional GLib.Cancellable  | 
            
| 
                 A new collection of GLib.File objects for each child file of the directory, or null if invoked on a file which is not a directory.  | 
            
| GLib.Error | 
                 if an error occurs while enumerating the children  |