Cannot require the library being an ES Module

[jp06]

I think it would be nice to have it work for both CommonJS require and ES Modules import. At least, the current readme implies you can do a require but you'll actually get a ERR_REQUIRE_ESM error when you follow the example code. As a workaround, one can do a dynamic import or change the package.json's type to module when using this library (what I did for my script).

I already generated my EPUBs and have imported them on my Kobo, thank you for your work on this fork!