babel-eslint parser option

[benmosher]

Need to investigate swapping in babel-eslint as the parser instead of the baked-in espree, as an option.

For those brave enough to use babel-eslint, this would continue to allow all the bleeding-edge experimental JS through without parse errors. (prompted by issue #36)

Best case: infer this setting from the .eslintrc/rule context.
Worst case: add an import/parser setting analogously to the setting in ESLint proper.