Support for set_scene

Hi Stavros! While browsing around I spotted a thread[1] about ceiling light's moonlight mode API, and looks like set_scene has not been implemented yet. I'm unsure if that method was always there in place (as discover_bulbs() doc indicate it was), was there some specific reason for not implementing that? If no (or it's just recently been documented), maybe it's worth to look into that at some point :-)

[1] http://forum.yeelight.com/t/enable-moonlight-of-yeelight-ceiling-with-api/1182