NNBD and more darty api

[KalilDev]

In dart, the convention is camelCase, final fields, and now, nnbd. The package needs an great migration. I did it at my github, but it is an humongous breaking change and contains 3 packages that i made and didnt publish to pub.dev. I tried to only migrate to nnbd but because the fields are set after object initialization, it proved to be rather chalenging. So as it was becoming an big breaking change with big consequences i ended up doing it my way.

[KalilDev]

So, how do we go from here? Do you have any intention on continuing to develop this package? Do you want me to retry the migration (although, because of the mentioned issues, most, if not all, the fields will be nullable)? Probably just keeping this package as an legacy one and not migrating is totally fine also, i just did it for an personal project, in which i also used a lot of private dart-epub apis, not the intended usecase of the package, so its kinda obvious that it bit me

[KalilDev]

Yeah, i just checked epubx, everything is nullable