feat(util/rb_tree): add unsigned_rev_cmp
feat(util/rb_tree): add unsigned_rev_cmp

avigad/lean,Kha/lean,rlewis1988/lean,Kha/lean,soonhokong/lean-osx,leanprover-community/lean,dselsam/lean,leanprover-community/lean,johoelzl/lean,fpvandoorn/lean,fpvandoorn/lean,leodemoura/lean,soonhokong/lean-osx,soonhokong/lean-osx,soonhokong/lean-windows,fgdorais/lean,leanprover/lean,Kha/lean,leodemoura/lean,leanprover-community/lean,digama0/lean,fgdorais/lean,johoelzl/lean,leodemoura/lean,leodemoura/lean,avigad/lean,fgdorais/lean,leanprover/lean,avigad/lean,leanprover-community/lean,Kha/lean,leanprover/lean,leodemoura/lean,fgdorais/lean,fgdorais/lean,fpvandoorn/lean,soonhokong/lean-windows,soonhokong/lean-windows,digama0/lean,leanprover/lean,soonhokong/lean-osx,leanprover/lean,dselsam/lean,digama0/lean,soonhokong/lean-windows,rlewis1988/lean,digama0/lean,soonhokong/lean-windows,avigad/lean,rlewis1988/lean,dselsam/lean,digama0/lean,johoelzl/lean,leanprover-community/lean,leodemoura/lean,leanprover/lean,avigad/lean,fgdorais/lean,Kha/lean,fpvandoorn/lean,fpvandoorn/lean,dselsam/lean,johoelzl/lean,johoelzl/lean,Kha/lean,rlewis1988/lean,rlewis1988/lean,rlewis1988/lean,dselsam/lean,fpvandoorn/lean,dselsam/lean,avigad/lean,digama0/lean,soonhokong/lean-osx,leanprover-community/lean,johoelzl/lean