modify amqp-consume to listen to multiple keys

I hacked this functionality in pretty quick, but I think it might be generally useful: https://github.com/brianin3d/rabbitmq-c/commit/1b0eb4893ac07d170a69ca10cebf152f29d5a3d8

It can be turned off by not defining ENABLE_MULTIPLE_KEY in tools/consume.c

Anyhoo...