Trace output distributions to a log file

[Piezoid]

I do not expect this to be merged, but I figured it might help others. Although, I don't know if this is the right place.

This logs information to a ./out.log (hard-coded) file. I wrote this throwaway code before the switch to stderr, which is why it uses a global file handle.
The refactoring of the sampler code should produce the same results than the master branch.

For each predicted token, it logs:

in:' because' n_past=14, remaining_tokens=62, embd.size()=1, embd_inp.size()=13
soft_max: top_sact=25.503617 mean_sact=19.826111 top_p=0.357196 entropy=1.664120
top_p: n: 15 sum: 0.990421
->0: ' they' p=0.357196 act=17.853 temp=0.70
  1: ' I' p=0.231013 act=20.643 temp=0.82
  2: ' of' p=0.228527 act=17.540 temp=0.70
[...]
  15: ' the' p=0.000876 act=13.645 temp=0.70

• The soft_max: lines reports statistics of the top k tokens' logits (divided by temp) and entropy (in nats, not bits),
• top_p: line gives the number of retained tokens after the top p filtering, and the sum of their probabilities,
• Last, a list of the top 16 tokens, along with their respective probabilities, original logits, and the product of their temperature and eventual repetition penalty.. The drawn token is indicated by an ->.

I will close this either when it becomes obsolete or when it can no longer be rebased.