make archiver returned data format easier to use when multiple PVs are requested

[ambarb]

Please see the notebook example in which 3 PVs are requested simulatentously. The PVs are returned in what seems be an object that all three are inside for each timestamp. It isn't clear to me how to properly access the data or if I am using it in the intended way.

The notebook details the issue. Using databroker 11

https://nbviewer.jupyter.org/gist/ambarb/6ef24854189e8b6e35da377f3e5a6795