add Fill operation to hydrology
Added spark project
Merge pull request #637 from lossyrob/spark-project

Added spark project
Renamed name in Operation.

Fixes #507
Merge pull request #638 from lossyrob/operation-name-rename

Renamed name in Operation.
Initial commit of isNoData and isData macros.

Still need to figure out how to make those functions import nicely
with just `geotrellis._`. Aims to fix #624
isNoData and isData macros in geotrellis package

Converted all comparisons to their macro equivalent

z == NODATA                -->  isNoData(z)
z != NODATAT               -->  isData(z)
java.lang.Double.isNaN(z)  -->  isNoData(z)
!java.lang.Double.isNaN(z) -->  isData(z)
Added unit test for very strange compiler break.
Fixed issue with BitArrayRasterData override of map.

This map was not lazy by default like the other maps.
In addition to this, the old implementation would blow up the compiler.
I don't know why.
Merge pull request #642 from lossyrob/BitArrayRDBug

Fixed issue with BitArrayRasterData override of map.
Merged in upstream BitArrayRasterData fix
Merge pull request #639 from lossyrob/isNoData-macro

isNoData and isData macros
remove asm dependency
Merge pull request #643 from ameetkini/remove_asm_dependency_2

remove asm dependency
Refactored RenderPng to not use Histogram, use ColorMap
Added renderPng and writePng RasterSource methods.
Merge pull request #644 from lossyrob/rendering

Refactored RenderPng; added renderPng and writePng RasterDataSource methods.
Added .flatten method to Operation.

Fixes #223
Removed comment
Merge pull request #645 from lossyrob/flatten

Added .flatten method to Operation.