WORKER_THREAD support for node-rdkafka

**Environment Information**
- OS [e.g. Mac, Arch, Windows 10]:
- Node Version [e.g. 8.2.1]:
- NPM Version [e.g. 5.4.2]:
- C++ Toolchain [e.g. Visual Studio, llvm, g++]:
- node-rdkafka version [e.g. 2.3.3]:

**Steps to Reproduce**
WORKER_THREAD with Kafka is giving `Module is not self register error`

**node-rdkafka Configuration Settings**
V.2.12.0

**Additional context**
I can see the branch with the required change. When can we expect this change in master?

[https://github.com/Blizzard/node-rdkafka/pull/857/files](url)

Start by reviewing pull request #857 and comparing its changes with the current master branch. Reproduce the WORKER_THREAD Kafka case described in the issue, then verify that node-rdkafka loads without the "Module is not self register" error; the linked pull request indicates that work is already underway.

Written by the indexing model from the issue text.