BiLock fairness guarantees (or lack thereof) are not documented

[Qix-]

Hi there, I noticed that the BiLock documentation lacks any mention of fairness guarantees.

Judging from the guard's drop code, it appears that a pending lock from the other half is always honored upon the guard being dropped, which would mean a strong fairness guarantee, but I just want to double check before opening a PR to document that. Is that the case?