v0.4.0 — say how a file is protected

Document.Protection() reports what a file said about itself on the way in: the method in words (RC4-40, RC4-128, AES-128, AES-256, or none for a file that declares a security handler and protects nothing with it), the handler's revision, the permissions it grants, and whether the password it opened with was the owner's — in which case those permissions do not apply.

Permissions gains Allows and String, so what a file grants reads as print, copy rather than as a bit pattern.

100% statement coverage.