[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.
It is easy to change 'acs-node' to 'acs', but it may be not so easy to change node.acs module name, since there are some dependencies. For example, current version and previous versions of Titanium are using all 'acs' not 'nodeacs'. I'm not sure if this may influence Titanium update and make chaos.
@negupta @baobeimm can you please make a decision on when and how we want to change node module name of node.acs cli (nettle) from 'acs' to 'node-acs'? After that, I may just follow its process to rename 'acs-node' to 'acs'.