Merge pull request Workiva#151 from azr/master

augmentedtree: add traverse func

Merge pull request Workiva#149 from jxguan/patch-1

Fix the bug where the capacity is incorrectly calculated.

Merge pull request Workiva#148 from Workiva/fix_multidelete

Sort keys before deleting.

Merge pull request Workiva#147 from jim-slattery-rs/fix_queue_poll_me…

…mory_leak

fix queue.Poll() memory leak

Merge pull request Workiva#143 from Workiva/immutable_b_tree

Immutable b tree

Merge pull request Workiva#142 from Workiva/queue_take_until

Fix index in take until.

Merge pull request Workiva#140 from nvanbenschoten/nvanbenschoten/loc…

…kedSource

Create lockedSource for use by SkipList

Merge pull request Workiva#135 from alexandercampbell-wf/update_readm…

…e_set

README: update to point to alternative Set impls

Merge pull request Workiva#137 from funny-falcon/selectable_future

futures/Selectable - future with selectable completion channel

Merge pull request Workiva#139 from mikeatlas/queue-peek

added queue.Peek() functionality