[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.
We could use prototype and put code outside this constructor, but those functions defined by prototype way can only be called from an instance. Actually, new acs-node-sdk supports both class level call and instance level call:
```
var myApp = new ACSNode.ACSApp(ACS_APPKEY);
myApp.Users.login({
    login: ACS_USERNAME,
    password: ACS_PASSWORD
}, function(err, result) {
    if (err) {
        console.error(err);
        return;
    }
    console.log('Logged in user: %j', result.body);
});
```
```
ACSNode.Users.login(ACS_APPKEY, {
    login: ACS_USERNAME,
    password: ACS_PASSWORD
}, function(err, result) {
    if (err) {
        console.error(err);
        return;
    }
    console.log('Logged in user: %j', result.body);
});
```
This is the main reason I didn't put those functions via prototype, but module.exports and instance's constructor.