as4pgc - new audio stego tool available!

[Clark Fieseln]

you may want to add a reference to as4pgc:

https://www.codeproject.com/Articles/5313626/Audio-Steganography-for-Pretty-Good-Concealing-AS4
https://github.com/ClarkFieseln/as4pgc
https://pypi.org/project/as4pgc/

This tool has some advantages when compared to the other 3 audio tools (MP3Stego, DeepSound, AudioStego):

+ generic method, thus several formats supported (MP3, WAV, FLAC, OGG,..) 
+ available as .exe, and as python module
+ available in PyPi for easy installation with pip
+ really works with MP3 formats (DeepSound seems not, AudioStego has really strong whistles!)
+ works in Windows and in Linux
+ plots to help tracking processing steps (useful for developers)

In its current version 1.1.0 it has some disadvantages:

- slow (hiding takes 3 to 20 times the audio time length)
- more distortion/noise than MP3Stego, but I am working on that