Rename gen_marshal_input() to gen_marshal(), because the generated
function marshals both arguments and results.

Rename gen_visitor_input_containers_decl() to gen_marshal_vars(), and
move the other variable declarations there, too.

Rename gen_visitor_input_block() to gen_marshal_input_visit(), and
rearrange its code slightly.

Rename gen_marshal_input_decl() to gen_marshal_proto(), because the
result isn't a full declaration, unlike gen_command_decl()'s.

New gen_marshal_decl() actually returns a full declaration.

Signed-off-by: Markus Armbruster <armbru@redhat.com>
Reviewed-by: Eric Blake <eblake@redhat.com>
Reviewed-by: Daniel P. Berrange <berrange@redhat.com>
Message-Id: <1442401589-24189-16-git-send-email-armbru@redhat.com>