Peter M. Groen / FlashMQ

Also fixes a bug in new interval calculation.

This prevents bugs because the calling context forgets it. A (small)
downside is that I have to make the Publish argument non-const. But,
that's exactly what it is then, so...

Not tested yet.

I'm simplying/merging the rec, comp and rel packets, but I'm not sure it will
work. Committing as a safe point.

Later: I got it done as planned. Testing qos > 0 and mqtt5 still needs
to be done more.

I think it's correct, but mosquitto_sub doesn't seem to support it, so I
can't test.

Also some other stuff I happen to see.

And one line about correlation data that was a bug.

This replaces the old style checking of expired sessions once every 10
minutes or so.

I need to decide what to do with getPublishData

and that disabled test needs repurposing.

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.

Also includes fixes to packet parsing that I couldn't make a separate
commit for.

When it comes to QoS 1, these things are still left, off the top of my
head:

- vector for qos queue? It helps with ordering and is CPU cache friendly.
- Store subscription QoS.
- Do retained messages have QoS?
- Give session client's name, to access it later.

Also materializes some concepts about MqttPacket.

Roughly...