minor change to reflect spark/ directory structure
RasterSplitGenerator changes:
1. Remove compression ratio
2. Add assertion for case when tileExtent.width > tilesPerBlock
3. Add test for 2
corrected RasterSplitGenerator behavior in corner cases
added license header to RasterSplitGeneratorSpec
Merge pull request #761 from ameetkini/partitioner

minor partitioner changes to handle corner cases