
- prime_count - needs the pc(#) option as well as pc(#,#)

- Consider adding Lehmer's method for prime count.  The only use I can really
  think of would be 32-bit machines.  I worry that the overhead of GMP would
  kill us, and some method using __uint64s, or even Math::Int64 would be
  faster.

- nth_prime

- GMP SQUFOF could use a better implementation, though low priority since it
  just isn't going to be the right algorithm for numbers > 2^64.  Mainly what
  it needs is to pay attention to the rounds argument.  Perhaps race.

- Add Riemann R function

- Tune and improve SIMPQS for our uses.  Check FLINT 2.3 for improvements.

- Write our own QS.

- The statics in ecm and QS won't play well with threading.

- ECPP: Perhaps more HCPs/WCPs could be loaded if needed?

- ECPP: The current implementation is FSP, which is fine for ~300 digits
  and smaller.  Switch to FAS, which is a much better solution for larger
  numbers.  To do FAS (Factor All Strategy), we want to lighten the factoring
  on the first couple stages.  Then we go through not doing find_curve, just
  looking for numbers we can use.  Backtrack as needed.  If we get to the
  end of i=0, raise the factoring stage number and do it again.  At the end
  we have a complete q chain, at which time we do find_curve for them all.

- ECPP: Another idea is related to Atkin/Morain's EAS.  When we have a large
  number, we can process more Ds, delaying the downrun.  We then use the
  smallest q we found.  Combine with lightened stage 1 factoring as above.
  This drops our q sizes faster, at the expense of more up-front time.
  I have this running, but for small numbers it doesn't matter much, and for
  large numbers it just highlights how much nicer FAS would be.
