Fix wasm-beep example on Windows by upgrading to Webpack 5

[danwilhelm]

Problem: The wasm-beep example fails to run on Windows, giving the error "digital envelope routines unsupported".

Solution: Upgrading Webpack from 3.* to 5.* resolved the error.

Note: This PR requires the "syncWebAssembly" option. The latest Wasm spec recommends "asyncWebAssembly" instead, but the Rust code would have to be updated to use this.

Testing: Successfully tested npm install/npm run/npm run build on Windows and Mac.

I also updated the Wiki here: https://github.com/RustAudio/cpal/wiki/Setting-up-a-new-CPAL-WASM-project