Fix ES6 default export

[webfrank]

Added ES6 export, can be used like:

import renderjson from 'renderjson

[andifreed]

Does that break ES5 support?

[rtritto]

Any update?

[rtritto]

@caldwell please can you merge this?

[caldwell]

Not as it stands, no. When try it on the test.html page I get this error:

Uncaught SyntaxError: export declarations may only appear at top level of a module

I'm not opposed to Ecmascript modules at all, but right this second I don't know how to make something compatible with commonjs and modules and just raw <script> sourcing in html.

Probably the right answer in 2023 is to just make it a module, and use esbuild or something to make the non-module version/minimized versions when prepping for npm publish…