Add Accumulation to hydrology operations
fixed Accumulation.scala in hydrology

changed from using two stacks to using tuples.
Removed Option[] from Raster.asArray,.mutable,.force
Add Accumulation to hydrology operations
fix formatting in Accumulation
fix whitespace in Accumulation

remove erroniuos file
Merge pull request #599 from Markko/hydrology

Hydrology: Accumulation
Merge pull request #601 from lossyrob/asArray

Removed Option[] from Raster.asArray,.mutable,.force
Fixing tests
Merge pull request #602 from lossyrob/asArray

Fixing tests for asArray change
Fixed asArray in DiffTask
Tabs -> Spaces
Merge pull request #603 from wzjchen/hydrology

Hydrology Op: Tabs -> Spaces
Minor README fixes.
Update version number in sbt example.
Merge pull request #604 from joshmarcus/topic/update_readme

Minor README fixes.