Moses: extend _perm_ratio in backwards-compat way.

It seems that the old code (a few months ago) build significantly
fewer pairs than the current code, and this strongly affects scores
and learning.  So extend the meaning of _perm_ratio in a backwards-
compatible way, so that this can be explicitly controlled and tested.
Merge pull request #200 from linas/moses

Moses: extend _perm_ratio in backwards-compat way.
Minor simplication of composite_score constructor
Add power diversity_parameters::dst2dp

When the diversity penalty is a probability (as the Tanimoto distance
sorta is) it makes sense to multiply it with the score (which should
rather be a probability too) rather than subtracting it. Then it also
makes more sense to have the diversity pressure be the pth-power of
the diveristy penalty.
Minor simplication of composite_score constructor
Fix bug and improve comments related to pthpower diversity_parameters::dst2pd
Merge remote-tracking branch 'origin/composite_score_extension' into origin-composite_score_extension
Add user option to multiply diversity penalty by raw score instead of subtracting
Increase version to 3.6.6 (new user option)
Merge pull request #201 from ngeiswei/composite_score_extension

Composite score extension
Fix precision_bscore::best_possible_bscore (offset by 0.5)
Remove extra space
Add . separator to distinguish expansion from breadth first index
Merge pull request #202 from ngeiswei/fix_demeID

Add . separator to distinguish expansion from breadth first index
Modify policy of option --max-candidates so that it actually works

Select the top max candidates ignoring redundant or invalid candidates
without race condition (indeterminism).

This was the previous behavior before I replaced it with something
that would not account for redundant or invalid candidates, except it
is deterministic.

So this potentially modifies the behavior of MOSES, you might want to
lower --max-candidates to get back to similar behavior in term of
number of candidates merged.
Set moses version to 3.6.7 because the behavior has slightly changed
Merge pull request #203 from ngeiswei/max_pot_cnd

Max pot cnd
Add initial test unit for scoring.{h,cc}
Complete scoring unit test
Merge pull request #204 from ngeiswei/fix_precision_bscore_best_score

Add precision bscore best score unit test