Peter M. Groen / FlashMQ

For the coming MQTT5 support, I'll need this a lot.

This is a preparation for MQTT5, because when there are receivers and
publishers with different protocols, you can't always just write out the
same packet. You can sometimes though, so that's what the copy factory
determines.

Because that's what's it is now.

A lot of code can be refactored to get the settings from this now, but
I'm not going to do that yet.

There were bugs in which authentication object was used when, causing
threadings bugs. Instead of getting from the 'sender', we can just store
a thread local pointer.

Files are simple serialized bytes prefaced by lengths. File is hashed to
verify integrity. This was also a good way preventing unexpected errors
when trying to crash the parser by having it load a different file.

This change includes some refactoring that was necessary:

- It 'fixes' looking at the wrong thread's authentiction. This is still
  wrong though. It will be fixed by a thread local pointer in the next
  commit.
- Deadlocks with yourself are handled in rwlockguard.
- QoSPacketQueue is now a class.
- Probably other tweaks.

Instead of getting it from the sender of a packet. Sometimes there was
no sender.

This fixes a crash on retained messages, because those newly created
packets didn't have a sender to get the threaddata from. So, using a
special object for it is easier and more robust.

I kind of need a config file parser first, so I'm going to make that.