[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.
As you can see from readme, we support instance mode, and this is [an example](https://github.com/realpaul/acs-node-sdk/tree/4b2ce65701a5bd0486be8b8540492b2eab1b15e5#create-an-instance-of-acs-app). We also [support direct call without instantiate an instance](https://github.com/realpaul/acs-node-sdk/tree/4b2ce65701a5bd0486be8b8540492b2eab1b15e5#straightforward-call), and this kind of straight call may be useful for some simple purpose.

Could you please let me know if we should keep this two, or just leave way of instance? Keeping this two maybe more flexible of use as right now, but code is a bit complex.