SYNOPSIS
  # assumes a GnuPG::Key or GnuPG::UserID or GnuPG::UserAttribute object in $signed
  my $signing_id = $signed->signatures->[0]->hex_id();
DESCRIPTION
GnuPG::Signature objects are generally not instantiated on their own, but rather as part of GnuPG::Key objects. They embody various aspects of a GnuPG signature on a key.OBJECT METHODS
- new( %initialization_args )
 - This methods creates a new object. The optional arguments are initialization of data members.
 - is_valid()
 - Returns 1 if GnuPG was able to cryptographically verify the signature, otherwise 0.
 - compare( $other )
 - Returns non-zero only when this Signature is identical to the other GnuPG::Signature.
 
OBJECT DATA MEMBERS
- validity
 - A character indicating the cryptographic validity of the key. GnuPG uses at least the following characters: ``!'' means valid, ``-'' means not valid, ``?'' means unknown (e.g. if the supposed signing key is not present in the local keyring), and ``%'' means an error occurred (e.g. a non-supported algorithm). See the documentation for --check-sigs in gpg(1).
 - algo_num
 - The number of the algorithm used for the signature.
 - hex_id
 - The hex id of the signing key.
 - user_id_string
 - The first user id string on the key that made the signature. This may not be defined if the signing key is not on the local keyring.
 - sig_class
 - 
Signature class.  This is the numeric value of the class of signature.
A table of possible classes of signatures and their numeric types can be found at http://tools.ietf.org/html/rfc4880#section-5.2.1
 - is_exportable
 - returns 0 for local-only signatures, non-zero for exportable signatures.
 - date_string
 - The formatted date the signature was performed on.
 - date
 - The date the signature was performed, represented as the number of seconds since midnight 1970-01-01 UTC.
 - expiration_date_string
 - The formatted date the signature will expire (signatures without expiration return undef).
 - expiration_date
 - The date the signature will expire, represented as the number of seconds since midnight 1970-01-01 UTC (signatures without expiration return undef)
 

