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