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.