Add the stripped, BSD licensed spec
Add the error 312

This is the error returned by rabbitmq when unroutable mandatory
publishings are undeliverable.
Fix synchronous flag of 'recover'.

This looks like an oversight in the spec, as recover-ok is synchronous
where recover was not.

The [json
spec](http://hg.rabbitmq.com/rabbitmq-codegen/file/31efa422585d/amqp-rabbitmq-0.9.1.json#l404)
indicates that recover is a synchronous method.
Use the BSD licensed amqp091 spec.

Goodbye comments :(
Merge branch 'bsd-spec'