[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.
Since javascript isn't strongly typed, functions with an arity greater than about 3 or 4 get a bit hard to handle (a strongly-typed language would fail with a type error at compile or run time, but JS will just do weird things). After that, it is usually much easier to pass them all together in one argument as a hash. This has the benefit of "naming" them such that any calls to the function (internal or external) will be easy to interpret without having to inspect the original function source or documentation. So it might look more like this:

```javascript
methodCall({
  acsObject: myAcsObject,
  appKey: myAppKey,
  // etc, etc
}, function(err, resp) {
  // callback still gets passed as it own argument
});
```