cbook deprecations

Many unused or near-unused cbook functions and classes have been deprecated:

``converter``, ``tostr``, ``todatetime``, ``todate``, ``tofloat``, ``toint``,

``unique``, ``is_string_like``, ``is_sequence_of_strings``, ``is_scalar``,

``Sorter``, ``Xlator``, ``soundex``, ``Null``, ``dict_delall``, ``RingBuffer``,

``get_split_ind``, ``wrap``, ``get_recursive_filelist``, ``pieces``,

``exception_to_str``, ``allequal``, ``alltrue``, ``onetrue``, ``allpairs``,

``finddir``, ``reverse_dict``, ``restrict_dict``, ``issubclass_safe``,

``recursive_remove``, ``unmasked_index_ranges``.