Peter M. Groen / FlashMQ

This required adding a global stats object.

It also contains a bit of refactor to make a type out of the derived
counters.

This fixes clients being disconnected after reducing the max value and
reloading the settings.

Check events are placed in a sorted map based on the last activity and
keep-alive interval of the client.

This makes it more accurate and reduces system load because it saves
unnecessary checking.

It merely drops packets when they exceed it. The specs are unclear about
whether you're supposed to delay transmission until the quota is
non-negative again. I decided against it because of increased
complexity, and because on a continously overloaded client, this makes
no sense.

Effectively, this formalizes the 'max qos pending' mechanism that was
already in place.

It also includes PUBACK/PUBREL/PUBCOMP error handling, because that
needed to be done for proper quota control.

The only thing it did was false trip the fuzzer.

Diff with 'ignore whitespace' looks clean.

This also contains some fixes/unifications for traditional
authentication, error handling specifically.

The CONACK indicated that it's not supported, and the specs say to issue
a disconnect when they're used after all.

This should prevent stale data from old clients from manipulating the
session.

This required a special type WillPublish to make this easier and more
logical.

It erroneously referred to the system function 'dup' now...

Also fix some bugs:

- The password can be binary data.
- The will topic is now also checked.

This allows easier saving of MQTT5 properties, for which a new file
version for retained messages is created. It uses the packet parsing logic.

It went over boundry when there were no properties.

Also changed will logic in disconnect: only clear it when it's a
successful disconnect.

- Delay is properly counted from moment of disconnect.
- When a session is picked up again, the will is not sent.
- An actual fix to what I tried a few commits ago: fix sending will
  twice.

This logic should make storing wills also easier.

I think it's very hard to distinguish between protocol error and
malformed packet. It's kind of arbitrary...

Also fixes a bug in new interval calculation.

And the TODOs are for the next thing: saving the createdAt date.

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...

Also fixed a length check bug.

Because clients can now also exist as dummy objects, I had to add some
extra checks.

Also split up handlePublish() and the new parsePublishData().

I'm not sure how I'm continueing. I need a safe point.

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.

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.