Add proof-of-concept classes: Master,Job, & Broker

See #1.

Master usage:

    master.py [-h] rep_uri

    Router-to dealer broker

    positional arguments:
      rep_uri

Broker usage:

    broker.py [-h] router_uri dealer_uri

    Router-to dealer broker

    positional arguments:
      router_uri
      dealer_uri

Job usage:

    job.py [-h] manager_uri

    Job demo

    positional arguments:
      manager_uri
Fill in README, rename Job -> Worker, see #1