Viewshed implementation
Update benchmark information
Created unit test for viewshed. Moved viewshed to op/global
Merge pull request #3 from lossyrob/feature/viewshead

Created unit test for viewshed. Moved viewshed to op/global
Update viewshed and tests
Prelim Approx Viewshed work. Has a bug that I'm not sure of the reason for
Fix, benchmark, and tests for approx viewshed
ApproxViewshed test coverage changes
Add BitRaster Comparator Ops
Merge branch 'raster-comparator' into feature/viewshed
Merge in cc9c033e03b7a60700be22a364de7a24f5d31915
Switch x/y and i/j to follow col/row convention. Handle NODATA and add test for it
Switch x/y and i/j to follow col/row convention for ApproxViewshed
Added Bounding Box, validation for all geometries, other changes.
Renames on result vars
Merge pull request #783 from jchien14/feature/viewshed

Viewshed implementation
Merge pull request #800 from lossyrob/feature-methods

WIP: Added Bounding Box, validation for all geometries, other changes to geotrellis-feature.
Packbits working.
Merged with master.
ZLib compression done.