Add es module

[YerkoPalma]

No description provided.

[goto-bus-stop]

I think this needs a protocol?

[YerkoPalma]

Something like this?

import assert from 'https://www.unpkg.com/nanoassert?module'

[goto-bus-stop]

yea. actually, doesn't unpkg automatically rewrite import paths when you use ?module? just doing import assert from 'nanoassert' might just work already.

[YerkoPalma]

It doesn't .Something like https://unpkg.com/md?module get resolved to https://unpkg.com/md@0.6.0/dist/md.es.js?module which is the actual version plus whatever you defined in your module property in package.json

[goto-bus-stop]

I mean how the import statements in the package source code get rewritten, like this:

so if we do import assert from 'nanoassert' here, unpkg would turn it into import assert from 'https://unpkg.com/nanoassert@x.y.z/index.js?module' automatically. bundlers could also use this entry point then.

[YerkoPalma]

Oh, you mean when already published? Actually never tried that, it would be much cleaner.

[YerkoPalma]

@yoshuawuyts @goto-bus-stop Thanks for your comments.
I've updated this PR with your suggestions and also used microbundle for bundling es and cjs bundles.
(Travis is failling with node 5 and 4, not sure what to do about it)