This commit allows to extract the metric name from the topic path. Now
it can be configured if all metrics are in a object in a certain topic
or if every topic contains exactly one metric. However, currently these
modes can not be mixed.
This should solve !26
TODO:
* Update documentation
* Add unit tests
As mentioned in https://github.com/hikhvar/mqtt2prometheus/issues/23, we
do not use any logging framework at all. This was fine for getting the
exporter startet. However, with inreasing load the logging must be
configureable. This PR is a start to replace all instances of
"log.Printf" with the zap logger. The current configuration parameters
are the log level and the log format (console, json). We might expose
the log configuration to the config file. But I think this is overkill
for the current state of the exporter.
The device firmware tasmota places the device ID in the middle of the
topic path. To support those devices to this commit introduce the
device_id_regex configuration. The old behavior of the last element of
the topic path is unchanged.
