Randomize the system stoeplitz key
One can prove that the Toeplitz matrix generated from a 16-bit seed is
invertible if and only if the seed has odd Boolean parity. Invertibility
is necessary and sufficient for the stoeplitz hash to take all 65536
Generate a system stoeplitz seed of odd parity uniformly at random. This
is done by generating a random 16-bit number and then flipping its last
bit if it's of even parity. This works since flipping the last bit swaps
the numbers of even and odd parity, so we obtain a 2:1 mapping from all
16-bit numbers onto those with odd parity.
Implementation of parity via popcount provided by naddy; input from miod,
David Higgs, Matthew Martin, Martin Vahlensieck and others.