[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 Simon for your suggestion, and I considered to use url / querystring, but it seems this string concatenation cannot be ignored. Moreover, we use another hash 'parsedBody' to pass all parameters into request body via node module request: https://github.com/realpaul/acs-node-sdk/blob/8fe63bf24693936a200ea61c38ea0e73abbed1e0/lib/rest.js#L42, as well as use JSON.stringify(reqBody) to pass parameters into querystring via node module request: https://github.com/realpaul/acs-node-sdk/blob/8fe63bf24693936a200ea61c38ea0e73abbed1e0/lib/rest.js#L35. I believe node module 'request' will deal with them correctly by using util and querystring.

For the querystring attached url, we only put appKey there, all other parameters will be handled by reqBody. So maybe it is not so necessary to use querystring module?