added tuning options

-ri nn  inital prime table count (defaults to 50000, range is 50000-500000 )
-ru nn upper prime table count (defaults to 120000 )
-rs nn is number of upper primes in chain to use higher number of primes to check (defaults to 3, so out of 6, it does 4, 5, and 6. if set to 2, it will start upper prime table for primes 5 and 6) 
-rm (no argument) whether to gradually increase from lower prime table count while stepping through the upper primes (default off)