WIP on introducing binary steal iterators.
A bunch of refactoring and work on binary tree stealers.
Implementing binary tree stealer advance.
First attempt at splitting, no tests yet.
Fixing the R*LL case for splitting.
WIP on SubtreeIterator
Merge remote-tracking branch 'origin/topic/simple-trees' into topic/simple-trees
SubtreeIterator done
style fixes + iterator duplication
WIP on comparison benchmarks
Merge branch 'topic/simple-trees' into topic/wip-tbb-comparison