Feature: Persist jobs as JSON

[gaebel]

Serialization

Seems this can't be achieved elegantly (because of polymorphism and generics). The consumer of the library has to provide the proper serializer for the task via a serializer module. This way custom serializers can also get registered. So basically there's no way to hide kotlinx.serialization from the outside (the outside depends on it).

val scheduler = JobScheduler(customModule = SerializersModule {
    polymorphic(DataTask::class) {
        subclass(TestTask::class, TestTask.serializer())
    }
})

See https://github.com/Kotlin/kotlinx.serialization/blob/master/docs/polymorphism.md

Persistence

Persists and restores jobs via SharedPreferences/UserDefaults.

---

Merge after #3

[gaebel]

To-Do (possibly in separate branch)

• Expose JobPersister Interface instead of third party Settings class
• Proper Coroutine job handling
• Allow automatically starting queue
• Improve and add more tests
• Look into concurrency
• Try serialization with a generic/base task serializer

[benjohnde]

LGTM, the 1 second delay is a bit string though, but I am cool with that :) you could investigate different values as well!

[benjohnde]

I guess we should just finalise a first version, use it in our apps and go public. It will naturally evolve over time. We can add the potential improvements as issues to leave them on our radar somehow!

[benjohnde]

LGTM!