Support the webpack v2

[owanturist]

Hey!
I just wanted write some code for support new version of webpack api, but I did something yet while I do it. There are some things like:

• Added .editorconfig for better support different code editors.
• Added and configured eslint with plugins.
• Mocha and chai were swapped to Ava. It make tests more pure and clear.
• Used temp for creating temporary directories and files for tests.
• Mock of webpack was swapped to real webpack instant in tests. But I could not support some test cases (like check dependency in watch mode).

There are changes in loader in general like this:

• I could not understood how the option maxInstances works. And I remove it from loader.
• Strategy of detecting watching mode was changed. It based on options of loader and memory file system.
• Promises were refactored and now they more clean and nice.

So, I hope, that you can to merge this pr in the future. And I will waiting for your questions and proposals about it.

Sorry for my English, but I'm trying to make the world of elm a bit better.

[eeue56]

I could not understood how the option maxInstances works. And I remove it from loader.

maxInstances is required for ensuring webpack does not crash in some situtations (multiple entry points). It can't be removed

Please split this PR up into small parts, and open new PRs. that will make it easier for me to review and merge.

[owanturist]

@eeue56 thank you for the response. I will do it.