Add an API around the build files to make it easier to use them

[DavidCks]

Right now, using piper just from the build files requires a lot of extra work.
This can be avoided by providing a simple interface to interact with PiperTTS.

I've forked this repo and built a basic API around it:
https://github.com/DavidCks/piper-wasm

I also own the "piper-wasm" npm package which I'm willing to transfer if you want it.