My old attempt at AVS_RBTREE
My old attempt at AVS_RBTREE

Summary: Needs extensive testing and whatnot, but may serve as a base when someone wants to implement an actual treeset.

Test Plan: some tests included

Reviewers: kfyatek, mkrawiec

Differential Revision: https://phabricator.avsystem.com/D3445

AVSystem/avs_commons,AVSystem/avs_commons,AVSystem/avs_commons,AVSystem/avs_commons