revert to 0.5.2-dev
revert to 0.5.2-dev

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