Add support for setting per-item FileOptions (mapping)

[m4heshd]

This PR implements the feature discussed in #12, allowing an instance of FileOptions to be set for each file or directory processed by create_from_directory_with_options(). As mentioned there, this API refactor would be a breaking change.

Current usage of the API:

let mut zip = ZipWriter::new(file);

// This has the limitation of only allowing one configuration for all the files and directories.
zip.create_from_directory_with_options(
    &PathBuf::from(&source_dir),
    FileOptions::default(),
);

API usage with this PR:

let mut zip = ZipWriter::new(file);

zip.create_from_directory_with_options(&PathBuf::from(&source_dir), |file: &PathBuf| {
    if file.eq(&PathBuf::from("dir/my_executable")) {
        FileOptions::default().unix_permissions(0o775)
    } else {
        FileOptions::default()
    }
});