module perl for generate cryptographic signatures for objects

 Object::Signature is an abstract base class that you can inherit from in
 order to allow your objects to generate unique cryptographic signatures.
 .
 The method used to generate the signature is based on Storable and
 Digest::MD5. The object is fed to "Storable::nfreeze" to get a string,
 which is then passed to Digest::MD5::md5_hex to get a unique 32
 character hexadecimal signature.