Return http manifest.

        The http manifest is the resource that defines a dataset as HTTP
        enabled (published).

def generate_http_manifest(self):
        """Return http manifest.

        The http manifest is the resource that defines a dataset as HTTP
        enabled (published).
        """
        base_path = os.path.dirname(self.translate_path(self.path))
        self.dataset = dtoolcore.DataSet.from_uri(base_path)

        admin_metadata_fpath = os.path.join(base_path, ".dtool", "dtool")
        with open(admin_metadata_fpath) as fh:
            admin_metadata = json.load(fh)

        http_manifest = {
            "admin_metadata": admin_metadata,
            "manifest_url": self.generate_url(".dtool/manifest.json"),
            "readme_url": self.generate_url("README.yml"),
            "overlays": self.generate_overlay_urls(),
            "item_urls": self.generate_item_urls()
        }
        return bytes(json.dumps(http_manifest), "utf-8")