Include tools for testing various parts of the app

Rename audio to corresponding audio event.

Provide latest versions of the files.

Update documentation.

Correctly dereference pointers.

Provide default states for input and output.

Allow MIDI input to be filtered through MIDI channels.

Restrict Yes/No actions in same 2-octave span.

The file has been updated upon introducing MIDI controller input
support.

Make device handling opt-in.

Ensure that initial loading of the config saves the values back to the
config file, in order to account for fallback values.