Publish weather data via MQTT messages

[adenoz]

This is core functionality.

To do this, we'll also need a seperate configuration file to set broker details. This is done, in #4

We'll also need to determine topic naming conventions.

Data should probably also be published with one data point to one topic rather than have one MQTT payload with all data in one json message. This will allow for easier later saving of MQTT messages into a database.

[adenoz]

This is now complete. All current weather is now published via hard coded mqtt topics. Later, this should become user configurable but for now it is all working. The program will not allow erroneous data types to be published which is part of the strong data types used via the structs and match statements.

The current mqtt topics, with associated data, are as follows:

• outside/weather/current-temp
• outside/weather/temp-feels
• outside/weather/min-temp
• outside/weather/max-temp
• outside/weather/humidity
• outside/weather/rain-today
• outside/weather/wind-kms
• outside/weather/wind-kts
• outside/weather/wind-dir

The mqtt client is 'rusqttbom'.

One final wrinkle, so far I haven't been able to get the mqtt broker port to take a variable from the configuration file so that is currently hard coded. However, the mqtt broker IP address is read in from the config.toml file.