Workaround for Typhoeus to persist cookie jar to disk

This is an attempt at fixing https://github.com/typhoeus/typhoeus/issues/291 (Cookie jar option is not writing file to disk)

It works in my use case and satisfies libcurl's recommended cleanup sequence (curl_multi_remove_handle, curl_easy_cleanup, then curl_easy_cleanup) though frankly I couldn't figure out why garbage collection is not automatically triggering curl_easy_cleanup without this workaround.