Add CMS signed receipt genration and verification docs.

=pod

=head1 NAME

CMS_sign_receipt - create a CMS signed receipt

=head1 SYNOPSIS

 #include <openssl/cms.h>

 CMS_ContentInfo *CMS_sign_receipt(CMS_SignerInfo *si, X509 *signcert, EVP_PKEY *pkey, STACK_OF(X509) *certs, unsigned int flags);

=head1 DESCRIPTION

CMS_sign_receipt() creates and returns a CMS signed receipt structure. B<si> is

the B<CMS_SignerInfo> structure containing the signed receipt request.

B<signcert> is the certificate to sign with, B<pkey> is the corresponding

private key.  B<certs> is an optional additional set of certificates to include

in the CMS structure (for example any intermediate CAs in the chain).

B<flags> is an optional set of flags.

=head1 NOTES

This functions behaves in a similar way to CMS_sign() except the flag values

B<CMS_DETACHED>, B<CMS_BINARY>, B<CMS_NOATTR>, B<CMS_TEXT> and B<CMS_STREAM>

are not supported since they do not make sense in the context of signed

receipts.

=head1 RETURN VALUES

CMS_sign_receipt() returns either a valid CMS_ContentInfo structure or NULL if

an error occurred.  The error can be obtained from ERR_get_error(3).

=head1 SEE ALSO

L<ERR_get_error(3)|ERR_get_error(3)>,

L<CMS_verify_receipt(3)|CMS_verify_receipt(3)>,

L<CMS_sign(3)|CMS_sign(3)>

=head1 HISTORY

CMS_sign_receipt() was added to OpenSSL 0.9.8

=cut

=pod

=head1 NAME

CMS_verify - verify a CMS signed receipt

=head1 SYNOPSIS

 #include <openssl/cms.h>

 int CMS_verify_receipt(CMS_ContentInfo *rcms, CMS_ContentInfo *ocms, STACK_OF(X509) *certs, X509_STORE *store, unsigned int flags);

=head1 DESCRIPTION

CMS_verify_receipt() verifies a CMS signed receipt. B<rcms> is the signed

receipt to verify. B<ocms> is the original SignedData structure containing the

receipt request B<certs> is a set of certificates in which to search for the

signer's certificate. B<store> is a trusted certificate store (used for chain

verification). 

B<flags> is an optional set of flags, which can be used to modify the verify

operation.

=head1 NOTES

This functions behaves in a similar way to CMS_verify() except the flag values

B<CMS_DETACHED>, B<CMS_BINARY>, B<CMS_TEXT> and B<CMS_STREAM> are not

supported since they do not make sense in the context of signed receipts.

=head1 RETURN VALUES

CMS_verify_receipt() returns 1 for a successful verification and zero if an

error occurred.

The error can be obtained from L<ERR_get_error(3)|ERR_get_error(3)>

=head1 SEE ALSO

L<ERR_get_error(3)|ERR_get_error(3)>,

L<CMS_sign_receipt(3)|CMS_sign_receipt(3)>,

L<CMS_verify(3)|CMS_verify(3)>,

=head1 HISTORY

CMS_verify() was added to OpenSSL 0.9.8

=cut