Make changes so that source works on Windows too

[OldBoyCoder]

I've been using the wav2sketch code to create some audio samples for my Dalek project. As I wanted to run it on Windows I made some changes so it can compile under both gcc and Visual Studio. Not sure if you're interested in the changes or not but I thought I'd offer them up.

Tested with Visual Studio 2022 and gcc on Debian Buster on Raspberry Pi Model B

Thank you for all the work on the code for the Audio card.