Siever

The Siever manages the segmented sieve process.

At any given time, it holds onto a single sieve segment. Thus, the siever should be used for a single lookup or traversal.

Sievers are built using 'chunkSize' and 'cutoff' parameters. These are passed along to any sieve segments they create. When possible, it's probably better to use methods on the companion object, which will instantiate a Siever for you with reasonable parameters.