proper random phrase generation. disappointing entropy when using the
-- 58 bits for 5 word long phrase selected from sequence of 57,000.

This is likely do to the small number of bigrams involving rarer words,
the low branch degree translates to low number of interesting paths.

Entropy should probably improve significantly with a grammar-based
generation model instead of bigram-based. This would also allow
simplify the generation, since thousands of 'equivalent' words could be
grouped into a single node.