Abstract class to extend for easier java interop.
This batcher numbers batches based on a Calendar, not just milliseconds.
strictly before the beforeBound, we use the before Batcher.
Batcher implementation based on a fixed-width batch of milliseconds.
Job state models the memory of when the next job should try to cover
The Batch is the fundamental work unit of the Hadoop portion of Summingbird.
For the purposes of batching, each Event object has exactly one Time (in millis).