Add "Working with Async JS Objects" post

This post introduces the `method-proxy-js` project which can be found
at:

  https://github.com/causes/method-proxy-js

Change-Id: I96de09229204cd0bcc760c8364acce22ab6e10d9
Reviewed-on: https://gerrit.causes.com/22947
Reviewed-by: Joe Lencioni <joe.lencioni@causes.com>
Tested-by: Joe Lencioni <joe.lencioni@causes.com>