Add rendered versions of the gnupg logo to artwork.

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common: Add put_membuf_printf.

* common/membuf.c (put_membuf_printf): New.
--

This is just a convenience function for easier code readability.

Signed-off-by: Werner Koch <wk@gnupg.org>
gpg: Change OID of Ed25519 and add Brainpool oids.

* common/openpgp-oid.c (openpgp_curve_to_oid): Change OID for
Ed25519.  Add brainpool OIDs.
(openpgp_oid_to_curve): Ditto.
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This change is required to the change in Libgcrypt.  Note that we will
likely use a different OpenPGP algorithm ID for EdDSA and thus the
current Ed25519 implementation will not stay with us.

Signed-off-by: Werner Koch <wk@gnupg.org>