rootStaticFiles
Instead of directly serving the whole static folder at `/:path*`:

https://github.com/ream/ream/blob/d96bae0f853a37b1d2955994f9ce1c73da92b24a/packages/ream-core/lib/index.js#L157-L165

We should still copy `static` to output folder and add an option `rootStaticFiles` to serve files in output folder to root path, eg:

`/_ream/favicon.ico` will also be served as `/favicon.ico` when you have `rootStaticFiles: ['favicon.ico']` 

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Furthur changes for folder serving strategy:

- `public` will be served through http server as `/public` (not sure why we need this)
- `static` will be copied to `dist/static` instead of `dist`, then you can access it via `/_ream/static`
- Importing static file in your app will generate files in `dist/assets` instead of `dist/static`