Deprecated the Anonymizer#execute method

Also its related methdos #add_exception and #add_folder were deprecated.

From now on, the preferred method of anonymization is to use the
#anonymize method, which takes 'data' as an argument. This argument is
very flexible, and can be either a directory, a file path, a DICOM
binary string, a DObject, or an array containing multiple elements of
these.