Attempt to improve performance.
Previous implementation happened to be very slow (on my laptop it took 5
minutes to read small pwsafe file and save it back). I profiled the code
and it turned out, this cost was totally dominated by the
Crypt::PWSafe3::random function (which on every call accesses system
random seed).
I replaced it with Bytes::Random::Secure which seeds using OS crypto but
afterwards uses embedded generator. Performance improvement is drastical,
the same read&save takes about half a second on the same laptop.
