Add lint script and rules

[darthtrevino]

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Add a lint npm script; there's a .jshint file here, but it's not being used. It may be worth looking into a strict eslint rule-set that makes sense for LTS versions of NodeJS (4.x, 6.x).

Some options may be: https://github.com/thenativeweb/eslint-config-es https://www.npmjs.com/package/eslint-config-airbnb

etc..

The airbnb config, while great, aggressively suggests bleeding edge features that need transpilation support from babel, so it may not be a great fit here.