Peter M. Groen / FlashMQ

Having threads creates instability for the fuzzer, and we don't need
them.

This can be called by a fuzzer like afl-fuzz.

When sending many 0xFF, it would overflow.

Found by using afl-fuzz.

This allows creation of multiple listeners, with different protocols
and/or SSL certificates.

Related change: settings is now a class that is copyable and assignable,
and is done so to each thread on reload.

Semi-related fix: fix crash in quit when multiple threads initiated it.
This came to light when testing the auth plugin settings.

And fixed an assert in CirBuf.read().

The ping/pong is actually untested at this point, because Paho (my test
client for now) doesn't do those. I wonder if any do, because MQTT
already has ping/pong.

Also changed the disconnect reason a little: it now shows them all, so I
don't have to worry about which one is more important.

And include some extra error conditions.

This includes a timer mechanism.

It also contains some related improvements that I needed:

* Show disconnect reason
* Fix the while condition for doing write() to avoid an unnecessary call
* Config reloading logic

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 reloading of settings, which re-opens the log file.

The test cases give a bunch of warnings, but that's the COMPARE macro's
fault. Let's see what to do...

The MQTT docs showed a wrong condition for checking malformed packets.

And, we have to grow buffers to MAX_PACKET_SIZE, otherwise we can't
process. I still have some inteligent buffer shrink logic in mind.

There still is a bug: writing a very big packet. I wrote the test case
already.

Because the connectionClose would set fd=-1, clients were never properly
removed from the map, because the fd is the key.

Also fixed a locking issue when an exception happened.

Also materializes some concepts about MqttPacket.

Roughly...