C++ and Python: parse ipaaca.conf in cwd or ~/.config/

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