Add CLI option to set the port

[timotk]

Solves #38

Set the port:

 data_formulator -p 5001

This will also give a --help option:

$ data_formulator --help

usage: data_formulator [-h] [-p PORT]

Data Formulator

options:
  -h, --help       show this help message and exit
  -p, --port PORT  The port number you want to use

[timotk]

@microsoft-github-policy-service agree

[Chenglong-MS]

this is fantastic, I'll update the document and redeploy. Thanks for the contribution!