Files:
	- "tug_whistle1.ogg", 
	- "tug_whistle1.ogg", 
	- "tug_whistle1.ogg", and
	- "tug_whistle1.ogg" 

These audio files adapted from an audio file provided 
by https://freesound.org/people/the_toilet_guy/ under
the CC-BY 3.0 (Attribution 3.0 Unported) License. 
As such, these files are also released under the CC-BY 3.0
License from this project.

CC-BY 3.0: https://creativecommons.org/licenses/by/3.0/