Reduce memory usage in the sieve

Currently, memory usage of the prime sieve increases linearly with the size of the interval `[lo, hi]`, while the number of primes only grows asymptotically as `(hi) / log (hi)`. Furthermore, L1 memory caching is not exploited.

By implementing a segmented sieve both problems can be addressed at once: lowering memory consumption and increasing speed (in C++ I noticed up to ~~10x~~ 5x better performance).

The current algorithm is basically:

1. Discover prime numbers `p` less than `√hi`
2. Cross off multiples of `p` starting at `p * p`.
3. Collect all prime numbers in `[√hi, hi]`

The suggested procedure is:

1. Discover all prime numbers `p` less than `√hi`
2. Divide `[√hi, hi]` into fixed size segments / smaller intervals (fitting L1 cache)
3. Outer loop: iterate over each segment
- Inner loop: cross off all multiples of all primes in the current segment
- Collect all primes in the current segment

You only need to store one segment (constant memory allocation) in step 2/3 and if the segment fits in L1 cache it is extremely fast, since you're iterating over it multiple times when sieving.

For reference see http://primesieve.org/