Windows support

We should make sure it works on Windows before release

// phase one — build with Snowpack
header('Creating unoptimized build...');
await exec(`rm -rf .svelte/build/unoptimized`);

[Conduitry]

Node’s fs.rmdir will not currently fail if you pass it recursive: true and the directory does not exist. It will emit a warning though in Node 15 saying that it will do so in the future, advising you to use fs.rm (which was added in 14.14). I’d probably be in favor of doing something like (fs.rm || fs.rmdir)('.svelte/build/unoptimized', { recursive: true }).

Edit: Actually, just fs.rmdir('.svelte/build/unoptimized', { recursive: true, force: true }) looks like it keeps everyone happy, and works on Node 12+.

[Rich-Harris]

Closing in favour of the more general issue for adding package tests — #18