Add support for webpacker

[do-you-dare]

Rails 6 uses webpack by default, and it seems that social-share-button doesn't support it yet. I seems to involve adding a package.json and publishing the project on npm. An example can be found here: ifad/data-confirm-modal#53, found on this webpacker issue: rails/webpacker#57.

Do you plan to support installing with webpacker?

[martintsan]

#189 #189 (comment)

[kwent]

Way too hacky. Should not require coffee-loader, should not require('some_erb_file.erb') and so on.

Js should be compiled and ready to be imported as require("social-share-button") directly.