[Bug-gnubg] Grade thresholds

[Albert Silver]

I received another query on GNU's generosity in its grades
(Supernatural, World Class, etc.) by a strong Brazilian player I
introduced to GNU. He loves it, and has commented on how much faster it
is to analyze matches or do rollouts with, but noted that it seemed more
generous in its grades than Snowie 4. I can pass the e-mail to you, but
should note it's in Portuguese. 

I'd like to pass on two possible requests therefore:

1) just tighten the thresholds by a notch, so that Supernatural is at
0.04, WC at 0.08, etc. 

OR

2) Allow users to customize the thresholds if they like, such as is
possible for the move-by-move error thresholds.

One might argue that this last option would mean sharing results would
give incompatible results, but frankly I don't spend my time passing
results around nor do I believe others do, so I don't think it's much of
an issue.

                                                Albert