add eslint, support node>=6.0.0, update document, fix minor bugs

[HMarzban]

I have a long interface list of my devices, and npm ip package gives me the wrong IP always,
So I dig deep into files project and find out that we can retrieve interface IP address by the name of interfaces, but not mention in the document, so update document and inline document of ip.address(name, family) function in lib.js.

I start using npm run test and npm fix but unfortunately face to lots of error, so I replace jscs and jshint with eslint and config base on standard javascript styles.

meantime, when I use Eslint, appear Nodejs warning and deprecate function that's used in ip package, therefore I replaced them with the new one which aims to Nodejs 6 and above.

#93, #86, #81, #80, #73, #67, #65, #59, #56, #21 fixed