add OpenOptions wrapper

[Emerentius]

Doesn't contain os-specific extensions, yet.

This also deprecates File::from_options as that seems to have only been defined to avoid wrapping OpenOptions.
That function could also be kept, but then it should work with both fs_err::OpenOptions and std::fs::OpenOptions. You'd have to introduce a new type parameter (breaking change) and some way to convert fs_err::OpenOptions to std::fs::OpenOptions (can't be AsRef btw, but Borrow would work).
I don't think it's worth it. It only exists in fs_err so the only people affected by deprecation are old users of fs_err. People migrating to the crate after this PR would never need the function.

[andrewhickman]

Looks good to me!

As a future extension we could customize the error message based on what flags are passed to OpenOptions e.g. "error creating file" instead of "error opening file".