Add jsnext:main field, use main for dist.
Add jsnext:main field, use main for dist.

* Use dist/hyperapp.js for main. This lets you require("hyperapp")
  in node directly without a compilation step since hyperapp.js is
  a UMD bundle.

* Add jsnext:main, use src/index.js for rollup/webpack.

* Use better tags.

* Be more explicit in rollup cli options.

* Add babel field with preset so jest can test src directly and
  create coverage results for each file.

Mytrill/hyperapp,Mytrill/hyperapp,tzellman/hyperapp