[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.
Thanks Jeff, and the reason I used arg1, arg2, instead of acsKey, options, because I think we will have to support oauth way (accessKey + secretKey) some days later, although Wei told me we will not want to support this for now.
If we support oauth way, it may contains 3 arguments, and it may have 4 kinds of use:
- ACSApp(acsKey)
- ACSApp(accessKey, secretKey)
- ACSApp(acsKey, options)
- ACSApp(accessKey, secretKey, options)

I'm not sure how we can name them well under 3 arguments, so I decided to use arg1, arg2 with a clear code comments above, instead of key and options.