Peter M. Groen / FlashMQ

But, this is a safe point before I will refactor it. I will remove the
appStartTime and session last touched. With the new queued removals,
this is no longer necessary.

Only mqtt3 though.

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.

which also has implications on how I think to handle 'queuePacketAtSub'

The behavior for MQTT3 clients in the same, but I replaced the term
'clean session' and described the behavior in MQTT5 terms, of 'clean
start' and an expiry interval.

Most of it is limits we already implemented non-standard compliant.

Especially remove the flashmq_auth_plugin_allocate_global_memory(),
which was an old idea.

This saves some allocations.

This also meant having to set the C++ standard to 2014.

The getCopy() methods of sessions and mqttpackets can't be changed,
because of access errors (private).