When generating, copy static files instead of requesting

[eyeseast]

I'm currently (as I type this) generating a static site that includes several large video files. There's no reason to send those, or any static files, through the request/response cycle when copying them to a destination directory would have the same effect.

This would probably require subclassing Frozen Flask's builtin freezer, specifically _build_one to decide whether an endpoint needs any actual processing.