Moving data buffer generation into data_entry.js.  Starting WriteBatch.
Adding support for atomic write batches.

Moving buffer generation into DataBuffer.

Finishing up batched writes.

Writing all hint file buffers on batch write atomically.  Performance boost.

Adding fsync to batch writes.

Adding tests for Medea#write

Changing batch semantics to update timestamp when the batch itself is written.
Merge pull request #23 from argo/batches

Support atomic write batches.