chunks: Chunks->ChunksIterable, ChunkIter -> ChunkIterator
chunks: add chunk and ChunkIndexable
update readme and docs with api changes
Remove old core directory

This isn't in use.  It somehow survived the 0.5 to 0.6 purge.
chunks: more explicit compute_one signatures

This conflicted with some generic Python signatures.
expr: Summary
expr: Reductions support Number interface
compute: python arithmetic
api: start dplyr frontend
add dplyr source
add dplyr tests
python: summary tees of data sources

issue - this is non-streaming
dplyr: hook summarize to Summary object
python: compute summary tees only when necessary
dplyr: summary now returns by, not relabel.  Edit tests
dplyr: add reduce to imports
chunks: rename chunk() to get_chunk()
Merge pull request #500 from mrocklin/doc-edits

update readme and docs with api changes
Merge pull request #499 from mrocklin/chunks-rename

Refactor Chunks
sql: name reductions after column_operation