C Flat api shared library

[aguerrieri82]

I've created a simple C API interface to make it easier to integrate sfizz with higher-level languages: https://github.com/aguerrieri82/sfizz/blob/develop/api/api.cpp

I also included a build script (for Windows) targeting Android:
https://github.com/aguerrieri82/sfizz/blob/develop/out-android/build.cmd

A sample usage in C# using NAudio:
https://github.com/aguerrieri82/OpenXrSDK/blob/dev/src/Engine/Sfizz/Test.cs

I think this could be useful for the whole community. If you want to rewrite it following your standards and integrate it into the main branch, I don't really like to fork and disperse the effort.