doc improvements, particulary dataset docs
doc improvements, particulary dataset docs

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