jshint ☛ eslint

From @csilvers email:

It took a bit longer than expected, but the new javascript linter, eslint, is now live in prod! You may start seeing lint errors you've never seen before.

Let me know if you find any of the new lint rules onerous or just ugly. We want to end up with lint rules that really help our codebase with minimal cost to developers.

To help with that, I've added some autofixing mojo into arc lint, to fix up some common lint errors. If your commit is suddenly running into lint problems when you run git commit, try running arc lint to see if it will help you out. If there are errors you're seeing a lot that there's no autofix for, let me know and I'll see how practical it is to add one.

Happy linting!