This address [REEF-6] and [REEF-25].
It changes the policy of sending requests to YARN RM from "one-request-at-a-time" to "one-kind-of-requests-at-a-time".
Contributed by John Yang <johnyangk@apache.org>
Closes #4
REEF-24: Adding LogScope

Adds classes to be used within a try() block that automatically log the beginning and end times of the block.

Contributed by  Julia Wang Julia Wang <jwang98052@yahoo.com>

Closes #10
Add timings

This addresses [REEF-28]: Timings are added to the various important event
handlers using the recently added `LogScope` classes.

The code was written by Julia Wang <Qiuhe.Wang@microsoft.com>

Closes #12