NCEP/NCAR monthly average maps.

A short time ago, while writing about the discrepancy between the NCEP/NCAR index and TempLS mesh, I made a temporary modification to the daily WebGL plot to show monthly averages. I've now formalised this. There is a black bar at the top of the date selector, and if you mouseover that, it will offer monthly averages. They are all there now, including the current month (to date). I expect this will be kept up to date.