Use more common partition algorithm
Use more common partition algorithm

This partitioning algorithm is more commonly implemented in eg. C, and
is a bit less readable, but a lot faster.  Takes a 500k row sort down
from 30 seconds to 4.

Signed-off-by: Johannes Löthberg <8398eb9892c5ab2ff439ca0b5e4b0706dd9ebef9@kyriasis.com>

kyrias/ironsort