Allow output of .WAV clips and/or spectrograms of detections.

[ses4j]

Hi - I think there's value in being able to write out clips and spectrograms from the detections file. I have a script I modified to work with the nighthawk output .csv, which is available here if anyone wants to try it:

https://github.com/ses4j/nfc-tools/blob/main/nfc-processing/getsnips.py

I didn't know the best way it might be integrated: as a separate tool? Separate but included in the package? As a subcommand of Nighthawk (like nighthawk clip ...)? With --wav-output? (My only issue with the last is then it wouldn't be possible to rerun with different options, etc, if you wanted more control...)

Thoughts?