Add `files` property to package.json

This ensures that the npm package only contains what is really needed.
Merge pull request #35 from mathiasbynens/fix-package

Add `files` property to package.json
Add .editorconfig
Reformat tests

Closes #34.
Merge pull request #37 from mathiasbynens/reformat-tests

Reformat tests
Merge pull request #38 from mathiasbynens/master

Add .editorconfig
Remove the `from` and `to` properties in favor of `range`

Closes #29.