Log Message:
Update to 0.73

Upstream changes:
0.73 2018-11-15

    [ADDED]

    - inverse_totient(n)              the image of euler_phi(n)

    [FIXES]

    - Try to work around 32-bit platforms in semiprime approximations.
      Cannot reproduce on any of my 32-bit test platforms.

    - Fix RT 127605, memory use in for... iterators.

0.72 2018-11-08

    [ADDED]

    - nth_semiprime(n)                the nth semiprime
    - nth_semiprime_approx(n)         fast approximate nth semiprime
    - semiprime_count_approx(n)       fast approximate semiprime count
    - semi_primes                     as primes but for semiprimes
    - forsetproduct {...} \@a,\@b,... Cartesian product of list refs

    [FIXES]

    - Some platforms are extremely slow for is_pillai.  Speed up tests.

    - Ensure random_factored_integer factor list is sorted min->max.

    - forcomposites didn't check lastfor on every callback.

    - Sun's compilers, in a valid interpretation of the code, generated
      divide by zero code for pillai testing.

    [FUNCTIONALITY AND PERFORMANCE]

    - chebyshev_theta and chebyshev_psi redone and uses a table.
      Large inputs are significantly faster.

    - Convert some FP functions to use quadmath if possible.  Without
      quadmath there should be no change.  With quadmath functions like
      LogarithmicIntegral and LambertW will be slower but more accurate.

    - semiprime_count for non-trivial inputs uses a segmented sieve and
      precalculates primes for larger values so can run 2-3x faster.

    - forsemiprimes uses a sieve so large ranges are much faster.

    - ranged moebius more efficient for small intervals.

    - Thanks to GRAY for his module Set::Product which has clean and
      clever XS code, which I used to improve my code.

    - forfactored uses multicall.  Up to 2x faster.

    - forperm, forcomb, forderange uses multicall.  2-3x faster.

    - Frobenius-Khashin algorithm changed from 2013 version to 2016/2018.