bpo-43420: Simple optimizations for Fraction's arithmetics

bpo-43420: Simple optimizations for Fraction's arithmetics

making Fraction class more usable for large arguments (>~ 10**6),
with cost 10-20% for small components case.

Before:
$ ./python -m timeit -s 'from fractions import Fraction as F' \
-s 'a=[F(1, _**3) for _ in range(1, 1000)]' 'sum(a)'
5 loops, best of 5: 81.2 msec per loop

After:
$ ./python -m timeit -s 'from fractions import Fraction as F' \
-s 'a=[F(1, _**3) for _ in range(1, 1000)]' 'sum(a)'
10 loops, best of 5: 23 msec per loop

References:
Knuth, TAOCP, Volume 2, 4.5.1,
https://www.eecis.udel.edu/~saunders/courses/822/98f/collins-notes/rnarith.ps,
https://gmplib.org/ (e.g. https://gmplib.org/repo/gmp/file/tip/mpq/aors.c)