modified:   exp/exp.py
- use pref_prob
- different temperatures
modified:   learner.py
- changing edge and changing it back ended up in wrong results because
  of rounding and normalizing, now copy used again - it is not as slow
  as KL distance, so doesn't really matter
modified:   automaton.py
- memoization now uses state indices, because a list of floats is way
  cheaper than a dict of (state_name, float) pairs

- memo is filtered when computing the generated language by small
  amounts without effecting the generated probability (as tested on some
  problems)