Update core checksum endpoint to output sha256 hashes

[nateinaction]

The ​plugin checksum project put up an endpoint which provides both md5 and sha256 hashes for plugin files. It would be nice if the api for core files provided sha256 checksums as well.

Current endpoint example: ​https://api.wordpress.org/core/checksums/1.0/?version=4.7.4&local=en_US
Current output example:

{
    checksums: {
        4.7.4: {
            wp-settings.php: "fb589663ae16319c1e228edf604125e9",
            ...
        }
    }
}

Suggested change - Add a 1.1 endpoint with the following example output:

{
    version: "4.7.4",
    local: "en_US",
    source: "https://core.svn.wordpress.org/tags/4.7.4/",
    zip: "https://wordpress.org/wordpress-4.7.4.zip",
    files: {
        wp-settings.php: {
            md5: "fb589663ae16319c1e228edf604125e9",
            sha256: "0a0cd31b875f8e1357ecbbb27906dfdec6f4bede01409cd70a4e8d5e5a9ce021"
        },
        ...
    }
}

Thoughts?