[NODEJS-1598] PoC of acs-node-sdk Rework

## Ticket Information
***JIRA Ticket***
https://jira.appcelerator.org/browse/NODEJS-1598

***Description***
This PR is about to raise a PoC of ACS Node SDK rework. It re-designs framework of acs-node-sdk, and supports multiple instances. It also provides a way to list all available ACS objects and methods including doc url for a good reference. Test framework with travis-ci is added too for a good and automatic test.

Since this is only a PoC, I only implemented ACS object "Users". If this way is towards to a good direction and passes code review, we will add all other ACS objects later.

## Get started
Please refer to readme file https://github.com/realpaul/acs-node-sdk/blob/NODEJS-1598_ReworkPoC/README.md for a general usage.
Grunt and JSHint has been included with the latest commits. Please refer to [Gruntfile.js](https://github.com/realpaul/acs-node-sdk/blob/4b2ce65701a5bd0486be8b8540492b2eab1b15e5/Gruntfile.js) and [.jshintrc](https://github.com/realpaul/acs-node-sdk/blob/4b2ce65701a5bd0486be8b8540492b2eab1b15e5/.jshintrc), and see if this is good enough. I have also modified code to pass JSHint with a more strict mode defined in .jshintrc. There is no error reported from grunt right now.

Please also let me know if you want to integrate other Grunt plugins into this project expect JSHint, and I will add them.