ROS backend depended on a mosquitto function, a stray copy-paste line ...

Added a verbose warning when trying to sniff on a global scope
on ROS - that is not implemented (needs 3rd party stuff (?)).
You need to specify a list of categories for now when using ROS.

Unreliable delivery during handshake phase persists.

The major caveat for ROS is potential message loss right
after a Publisher is advertised. tcp_nodelay has been set
in the Subscribers and latching in the Publishers (resending
the last message on demand to late Subscribers).
These are not completely airtight fixes, though.

I combined the source files & added skipping whitespace & a C++ wrapper.
Original source: https://github.com/littlstar/b64.c

The C++ parser is very minimal and ignores section markers (in our
case there isn't really any need for different sections anyway).
Python expects one section [ipaaca] - the format of the files
is otherwise standard ConfigParser / ini:

[ipaaca]

transport.mqtt.host=localhost
transport.mqtt.port=1883

backend=ros

You can override any of those using an environment variable
e.g. IPAACA_TRANSPORT_MQTT_HOST for transport.mqtt.host

Backends are automatically detected at module initialization.
There will be a warning if more than one is available and
you didn't specify the backend config key, e.g. using the env:
export IPAACA_BACKEND=ros
or
export IPAACA_BACKEND=mqtt

TODO: ROS host / port configuration etc (but rospy probably
honors their normal env vars internally; not tested)

It would need major reimplementation.
Note that this means the C# / .NET Windows version is also out
for now, since it relies on an IKVM wrapper around the jars.

Requires some preparations of the lib dependencies;
prepackaged compiled ipaaca libs ought to be provided.

Py and C++ confirmed to work on Raspberry Pi/ARM

TODO: config files for all versions

Mental note: MQTT backend (seen in Python) needs threaded event delivery

Some reusable refactoring into generic BackEnd possible

(Stress tests obviously needed.)

Always recovers auto-magically but at the cost of a minute or so
until finally live ... maybe related to error patched in Python version.

A one-line change for paho/mqtt/client.py from python-paho-mqtt.

(still unconnected to actual MQTT in this commit!)

Added conversion of JSON number format to int.

See merge request !1