RedisList: other operations on a wrong-type key leak a raw ResponseError; memoryview elements in lists #15

Minor findings of the review of #14, left out of its scope: (1) on a key holding a string/hash, getitem, slices, len, iteration, append, extend, insert, pop raise a raw WRONGTYPE ResponseError while [i]=/del now raise TypeError: make them consistent; clear() deletes a string key unchecked. (2) bytes-like elements of a list (e.g. a memoryview cast to 'I') go through the list codec unnormalised and corrupt the request (redis-py sends len instead of nbytes); normalise bytes-likes in _list_codec as #14 does for top-level values.