ConfigListener (Providence Utils : Config 1.7.0 API)

Functional Interface:

This is a functional interface and can therefore be used as the assignment target for a lambda expression or method reference.
```
@FunctionalInterface
public interface ConfigListener<M extends net.morimekta.providence.PMessage<M,F>,F extends net.morimekta.providence.descriptor.PField>
```
Interface for handling reactions to update of a config message.

- Method Summary
  
  All Methods Instance Methods Abstract Methods
  Modifier and Type Method Description
  
  void onConfigChange(M config)
  Called when the config is updated.

- Method Detail
  - onConfigChange
```
void onConfigChange(@Nonnull
                    M config)
```
    Called when the config is updated. Does not necessary mean the config did change it's values.
    
    Parameters:
    
    config - The new config instance.