Add secs tests equalization

[1DWalker]

Adds --equalize_test_with_non_secs flag to test secs models on the same reviews as non-secs models.
See: #149.

Model: FSRS-5-secs-equalize_test_with_non_secs
Total number of users: 100
Total number of reviews: 2097825
Weighted average by reviews:
FSRS-5-secs-equalize_test_with_non_secs LogLoss (mean±std): 0.3841±0.1827
FSRS-5-secs-equalize_test_with_non_secs RMSE(bins) (mean±std): 0.0793±0.0377
FSRS-5-secs-equalize_test_with_non_secs AUC (mean±std): 0.6981±0.0752

Model: FSRS-5
Total number of users: 100
Total number of reviews: 2097825
Weighted average by reviews:
FSRS-5 LogLoss (mean±std): 0.3761±0.1779
FSRS-5 RMSE(bins) (mean±std): 0.0687±0.0339
FSRS-5 AUC (mean±std): 0.7080±0.0744

[L-M-Sherlock]

LGTM

[Expertium]

@L-M-Sherlock this is good, but I still need a way to not calculate the loss on same-day reviews, neither in training nor in evaluation. So I want you you to add a flag for that.

[L-M-Sherlock]

@1DWalker would you mind developing that?

[Expertium]

Is it that difficult? I mean, it's just FSRS-5 with fractional intervals. Take FSRS-5 code (including the optimizer code), change the intervals and that's all.

[L-M-Sherlock]

I'm working on other things.