Add units conversion with rotation unit tests.
Add units conversion with rotation unit tests.

msalsbery/openseadragon,avandecreme/openseadragon,seanich/openseadragon,jmnetus/openseadragon,rdlester/openseadragon,openseadragon/openseadragon,seanich/openseadragon,msalsbery/openseadragon,LarissaSmith/openseadragon,avandecreme/openseadragon,jmnetus/openseadragon,rdlester/openseadragon,openseadragon/openseadragon,LarissaSmith/openseadragon