Partitioner improvements:
1. Use compression to estimate number of tiles that can fit onto a block
2. Cap the number of blocks per split to 1. As a result, support
intra-row splitting.
add RasterStorageStats
remove Tuple2 / Tuple3 for idiomatic purposes
add isCompressed to RasterStorageStats
Merge remote-tracking branch 'upstream/master' into partitioner_changes
Merge pull request #776 from ameetkini/partitioner_changes

Partitioner changes for supporting very large rasters