Add support for using via webpack

[anero]

Hello,

Would it be possible to add support for using JS code via webpack?
We started doing some of this work, adding a package.json file and modularizing jquery.remotipart.js and jquery.iframe-transport.js, but haven't been able to figure out how to include the iframe transport code into remotipart in a way that works both, with webpacker (i.e.: import {} from './jquery.iframe-transport.js') and assets pipeline (i.e.: //= require jquery.iframe-transport.js).

We've limited experience with JS modularizing so if anyone else has pointers on patterns for this use case, would be glad to wrap the work and submit a PR.

Thanks!

[anero]

Update on this: we've just submitted a PR with changes for supporting usage via webpack - #201