Added schemes to pool observations for parameter estimation

* Changed PoolerElevation to use bin edges, instead of fixed interval
* Added pooling by lat/lon boxes
Improvements to graphics2

* Added median absolute error metric
* Added -dpi switch
* Added '-type maprank', which show locations that have the
  lowest and highest score
* Allow '-leg' to take process unicode characters
Added 'fraction' option to CorrectorQuantileQuantile