Add NormalScaldingStore which contains only (K, V) pairs.
Merge branch 'develop' into klin_scalding_only_store
Address Oscar's comments.
Really add DirectoryBatchedStore.
Remove unused import in ScaldingStore.
Get rid of var Set of BatchID.
Address Oscar's comments.
Fix exclusiveUB.
Merge pull request #407 from twitter/klin_scalding_only_store

Add NormalScaldingStore which contains only (K, V) pairs.