Make generated results stable

Allow two chains with identical internal state to produce identical
output with the same random seed, and enable this behavior by default.

Since Perl randomizes hashes, two different instances of the "same"
chain can produce different output. This is due to iterating through the
key/value pairs of the probability hash in whatever order keys function
returns. Simply sorting the keys (with a stable sort) before iterating
allows for reproducible results.
Bump $VERSION to v0.008