Add wasm support

[dtbuchholz]

It'd be nice if you if you could use this library when compiling to wasm. E.g., in raf.rs, it starts off with these imports:

#[cfg(windows)]
use std::io::{Seek, SeekFrom};
#[cfg(unix)]
use std::os::unix::fs::FileExt;
#[cfg(windows)]
use std::os::windows::fs::FileExt;
use std::{fs::File, io, io::Write, path::Path, sync::Arc};

This is problematic since a wasm build will try to use the #[cfg(windows)] flag and cause errors downstream.