- Examine behavior near 32-bit limit on 32-bit machines.
  (done for factoring)

- GMP versions of all routines.

- segment sieve should itself use a segment for its primes.
  Today we'd need sqrt(2^64) max = 140MB.  Segmenting would yield under 1MB.

- Add test to check maxbits in compiled library vs. Perl

- Figure out documentation solution for PP.pm

- Is the current PP.pm setup the way we want to do it?

- Faster SQUFOF

- better prime count upper/lower bounds:
    - Dusart 2010 "Estimates of Some Functions Over Primes without R.H."
    - Schoenfeld or Stoll for with-RH limits

- Move .c / .h files into separate directory.
  version does it in a painful way.  Something simpler to be had?

- finish test suite for bignum.  Work on making it faster.

- After the factoring changes, we need to use Devel::Cover again to ferret
  out numbers that pass the early tests.