This fixes https://github.com/prettier/prettier/issues/42. It adds support for .editorconfig's `indent_style`, `indent_size`, `tab_width`, and `max_line_length` properties. It doesn't support the `end_of_line` property as described in https://github.com/prettier/prettier/issues/42#issuecomment-327073326, but that could be added later. The same goes for `quote_type` (https://github.com/prettier/prettier-atom/issues/293#issue-267288335). * Make test .prettierrc not set config for all file extensions This makes it easier to keep tests isolated.