Consistent logging of modification/read operations

[alexowens90]

For read-like operations (read, batch read, head, tail) logging the data that is attempted to be read in a consistent manner would aid debugging in production environments, at DEBUG level or lower as it would be very verbose, particularly for batch read operations with a lot of symbols. Similarly, when writing/appending/updating, logging the operations in a consistent manner would be useful, again at DEBUG level or lower, definitely including whether the item is being pickled or not. At VERBOSE level could also include the dataframe being written as well.