Chunked into

This uses chunking to move data between types that may extend beyond memory.

TODO

- [ ] Support `PyTables`
- [ ] Support `h5py`
For better or worse we end up passing around biggish `kwargs` bundles, elements of which are often unnecessary.  E.g. `into(foo, TableExpr)` might pass around `dshape-discover(TableExpr)` whether or not it is required.