(This is the first developer release for 2.0000.)

• THIS VERSION CHANGES THE FILE FORMAT.
  
  • Databases from DBM::Deep 1.0003 and higher can still
    be opened.
    
  • Newly-created databases automatically use the version 2.x
    format (numbered 4 internally), which version 1.x
    cannot open.
    
  • The optimize method, since it copies everything to a new
    database, upgrades it.
    
  • There is a new db_version method.
    
• Support for perl 5.6 has been dropped. We now require 5.8. 5.6
  users can still use version 1.0025. If anyone really needs 5.6
  support in version 2.x, we can add it back again, but would pre-
  fer not to. Bug fixes may be back-ported to 1.002x if requested.
  
• The File back end now supports Unicode. This is only supported
  for new databases. Old databases in the DBM::Deep 1.0003 format
  will have to be upgraded for this to work.
  
• New external_refs mode, which allows objects retrieved from the
  database to hang on to the corresponding database entries, keep-
  ing them alive, even after all references to them from the data-
  base itself have been deleted.
  
• Numeric comparison of DBM::Deep objects now works. Different
  objects used to compare equal. And there were uninitial-
  ized warnings.
  
• Deletions now work properly in the DBI back end. Deleting an
  array or hash referenced by two keys in the database used to
  be a no-op.