AMQP-CPP 2.1.2

This release contains a number of bug fixes, and a couple of small new features:

• There was a problem with methods being called on Channel or Connection objects that were already in an invalid state. In such a situation, an error was not always correctly reported to the Deferred object. This has been fixed..
• Building the library on Apple systems was not possible because it depended on header files that are not available on such systems. This has been fixed.
• New feature: the setQos() method now supports an extra parameter "global" to specify whether the quality-of-service applies to all consumers on the channel in total, or for each consumer individually.
• Empty messages (message with no body) were ignored by the library. This has been fixed.
• New feature: the Connection::parse() method can now also be called with a "Buffer" instance instead of a "const char *". This Buffer class is a base class with pure virtual methods that can be extended by the library user, and that can be more optimized than passing a contiguous buffer of bytes.