This branch, based on ngspice-32+ from pre-master branch on 25.07.2020,
contains functions to read, simulate and output wav audio files.

The origin of the code stems from
http://gareus.org/oss/spicesound/start
http://gareus.org/oss/spicesound/examples
mady by Robin Gareus, enhanced by Hannu Vuolasaho at
https://sourceforge.net/p/ngspice/patches/13/

It uses the external libraries libsndfile and libsamplerate-0.1.9.

The current setup has been tested only with MSVC 2019 on Windows 10.

libsndfile has been downloaded from http://www.mega-nerd.com/libsndfile/ as
http://www.mega-nerd.com/libsndfile/files/libsndfile-1.0.28-w64-setup.exe

libsamplerate-0.1.9 has been downloaded from http://www.mega-nerd.com/SRC/download.html as
http://www.mega-nerd.com/SRC/libsamplerate-0.1.9.tar.gz, and compiled
with mingw gcc 10.2 for 64 bit Windows 10. libsamplerate.lib has been created 
from libsamplerate.def by command
lib /def:libsamplerate-0.def /out:libsamplerate-0.lib /machine:x64
in the Visual Studio 2019 Developer Command Prompt.

The usage is described in
http://gareus.org/oss/spicesound/start

A complete package for Windows will be made available from the ngspice web pages.
Test on Linux and macOS will follow.