Started on focal operations.
Focal operations tested and fully working. Also moved some tests from engine to raster.
Merge branch 'master' into focal-ops-spark
Initial implementation of elevation operations in spark done.
Spark elevation works and test framework for testing single raster ops vs spark ops done. Need to fix serializations.
Elevation and Focal Operations done and tested.
Fixed broken test cases in focal.
Changed some function names and added a tailrec optimization.
Fixed hillshade and slope to have non-parantheses methods.
Merge pull request #934 from johanstenberg92/elevation-and-focal-ops-spark

Elevation and focal ops spark