per-hashes-file salt instead of per-secret salt

[philsnow]

If I understand correctly, a blueflower hashes file contains a single salt that is used for all the secrets in that file.

An attacker would have to recalculate rainbow tables once (taking into account this one salt) to then efficiently try to reverse the hashes in the file. A salt-per-secret model would be stronger.

[veorq]

That could be an optimization indeed, I may implement it later, or happy to take a PR :)

[JulesDT]

I think the PR above (#8) fixes this issue :) Can be closed

cc @philsnow