* add cli args --config, --debug and --verbose
load_config() will search for a relevant config file in several dirs
add separate handler methods for mute,unmute and toggle
mapping.toml removed, everything merged into config.toml
* add cli options subsection
* rename event variable to make it clear we're waiting for a stop event (and not some other obs event)
* fix argparse description
* add return None (for type checker)
* fix example in top level docstring
* add shorthand `-c` cli option
