[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.
Before that I referred to Stratus code, and at Stratus side we mostly used like:
```
var getACSCollection = function() {
};
exports.getACSCollection = getACSCollection;
```

But after reading some article, I think it will be better to use module.exports instead of exports, since they are not the same.
Some of blog entries just recommended like:
```
exports.getACSCollection = module.exports.getACSCollection = getACSCollection;
```
When initializing this PoC I used this style:
```
module.exports.function1 = function1;
module.exports.function2 = function2;
exports = module.exports;
```
Just for purpose of conciseness. I have updated all places with exports, and will follow the style of:
```
var getACSCollection = function() {
};
module.exports.getACSCollection = getACSCollection;
```