https://blog.offline-net.com/2010/09/11/thunderbird-lightning-provider-for-google-calendar-%e3%81%ab%e3%82%88%e3%82%8b-google%e3%82%ab%e3%83%ac%e3%83%b3%e3%83%80%e3%83%bc%e3%81%a8%e3%81%ae%e9%80%a3%e6%90%ba/