add weighted seasonal means example ipython notebook
add weighted seasonal means example ipython notebook

shoyer/xray,pydata/xarray,markelg/xray,markelg/xray,jhamman/xray,cpaulik/xray,kjordahl/xray,drewokane/xray,jhamman/xarray,markelg/xray,jhamman/xarray,jhamman/xarray,cpaulik/xray,pydata/xarray,shoyer/xarray,rabernat/xray,kjordahl/xray,pydata/xarray,chunweiyuan/xarray,jcmgray/xarray,NicWayand/xray,rabernat/xray,petercable/xray,shoyer/xarray,xray/xray