Change seed from 1 to 0 for better compatibility.

As suggested by Damian Gryski, compatibility with other implementations
does matter. The change obviously breaks the backward compatibility.

The most embarrassing part being that I can't remember why `1' was
chosen at first, but I mainly suspect a misunderstanding of Go's
stdlib hash interface (thought 1 was to be preferred to 0).

Closes issue #3.