Adds compiler loading for to-js languages in a similar fashion to Webpack itself

[gausie]

As mentioned in #102, this brings eslint-plugin-import in line with Webpack's own config loader.

[benmosher]

Can you add tests?

I.E. an additional extra folder like https://github.com/benmosher/eslint-plugin-import/tree/master/resolvers/webpack/test/files/some with an ES6 config.

[gausie]

Sorry that I haven't been able to do this. If someone else is able to (@kentcdodds if you're looking into this also?) that would be great.

Otherwise hopefully I'll have some time this week

[kentcdodds]

Sorry, decided that we're actually just going to be upgrading to Node4 this week anyway, so we're not going to be using the webpack.config.babel.js filename anymore anyway. Feel free to close #194.

[benmosher]

agh, didn't realize this commit wasn't properly part of #278, would've rebased onto it for proper credit. that said, was just published as v0.2.2 of the webpack resolver and you're credited in the change log 😅

[gausie]

@benmosher not a problem and thanks!