Peter M. Groen / FlashMQ

It's also used to reload settings. Settings are copied to threads, to
avoid concurrency issues.

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 some side issues.

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

Connected to this is preventing duplicate subscriptions. It's a bit
unclear what to do when you get a subscription for the same topic with a
different QoS? Change the Qos? Ignore?

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.

In preparation for clean session and qos.

It can be defined in the config file, along with options.

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

This saves mildly costly calls to find().

It's a little faster.

We use epoll now to change readiness.

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.