* (BREAKING) Changed the shelf backend from the default auto-select to dumbdbm (increases
portability and makes behavior more predictable. Fix by either selecting the appropriate dbm
or converting the files manually to dumbdbm)
* Added behavior to pass a backend to use (e.g. dbm backends, or a dict variable if you want
to make an in-memory database)
* Added backup function for backing up live databases or for the purpose of database recovery
(less efficient than copying files, it copies by keys, helpful for checking integrity)
* (FIX) actually enable writeback mode
* (BEHAVIOR CHANGE) entries now return an empty dictionary by default instead of raising a
KeyError
* Keys are now automatically convert to strings (via str())
* (BREAKING?) CSV import matching routine changed to avoid odd conversion of integers into
dates