Add Raster unit test for creating Rasters from an image and Bounds.
Add some docs to new raster algebra methods.
Add Bounds.getAspect() method.
Layer.getRaster() instead of Layer.toRaster().
Add another test to the MapAlgebra class.
Sync Raster support with Justin's work.  Lots of good stuff.
Fix failing unit test due to Raster.eval refactor.