'Stream' API: io.{Reader,Writer}
Fix siphon return + mark TODOs
Update documentation
Attempt to improve cached Read performance
Drop NopCompression for benchmark reasons

It caused an order-of-magnitude slowdown in pure cached reads.
Fix brainfart Reader Compression check
Fix + test for keys that resolve to directories
Warning to README
Merge pull request #3 from peterbourgon/streamwise

'Stream' API: io.{Reader,Writer}