thought this support already existed, but found out I was wrong when I
tried to make it work. :/) Applications for this include compression
and encryption.  An example wrapper storage implementation,
ZODB.tests.hexstorage, was included for testing.

It is important that storage implementations not assume that
storages contain pickles.  Renamed IStorageDB to IStorageWrapper and
expanded it to provide methods for transforming and untransforming
data records.  Storages implementations should use these methods to
get pickle data from stored records.