JS styleguide: Replacement for onevar

[jzaefferer]

As @timmywil commented on #105 (comment):

We need a replacement for this and I think it should be for all projects. I'd like to be able to enforce some value for http://jscs.info/rule/requireMultipleVarDecl.html or http://jscs.info/rule/disallowMultipleVarDecl.html and that should probably be included in the jquery preset.

Airbnb has decent rules for variables: https://github.com/airbnb/javascript/tree/master/es5#variables
ES6 variant: https://github.com/airbnb/javascript#variables

Are there other references we should consider? @timmywil would you be willing to put a draft together?

[arthurvr]

I'd personally prefer to put on the disallowMultipleVarDecl option 👍