use es6 module syntax

[sualko]

This is a first proposal to fix #63. There are still some todos:

• [ ] fix intention
• [ ] use npm packages if possible (requires rollup-plugin-node-resolve to create a browser bundle)
• [ ] ww tests fail for unknown reason
• [ ] npm prepublish hook to create bundles
• [ ] maybe move all export statements to the end of a file

What do you think?

[sualko]

@arlolra can you look into this?

[arlolra]

I'm currently travelling but hopefully soon.