elm-format distribution

In the long term, it makes sense to me for `elm-format` to be included with Elm platform. This is what gofmt did, after all. However, I can also see some benefit to having it being a separate package, installable via npm. I would also like to make a node interface to it, so that I can hook it up to webpack and enforce elm-formatted code regardless of platform.

I'm happy to do the leg work here. Just wanted to hear your thoughts @avh4

Review the proposed long-term distribution options: bundling elm-format with the Elm platform versus keeping it as an npm-installable package. The issue also proposes a Node interface for webpack integration, but names no files, tests, entry points, or acceptance criteria, so the desired outcome needs maintainer clarification first.

Written by the indexing model from the issue text.