Support minSdk version 24

[jeongth9446]

First of all thank you for open-sourcing such a great library.

My application is needed to setup in Android Nougat(SDK 24)
However, the library seems to be running from SDK 26 and above.
It seems that the date-related classes (DayOfWeek, etc.) have SDK 26 dependency.

Is it possible to support SDK 24 by modifying that?

[jeongth9446]

When below code applied, your library work well in lower version SDK!

I think it would be good to add the code below to the readme.

android {
defaultConfig {
// Required ONLY if your minSdkVersion is below 21
multiDexEnabled true
}

compileOptions {
// Enable support for the new language APIs
coreLibraryDesugaringEnabled true
// Set compatibility to Java 8 (can be higher if desired)
sourceCompatibility JavaVersion.VERSION_1_8
targetCompatibility JavaVersion.VERSION_1_8
}

kotlinOptions {
// Also add this for Kotlin projects
jvmTarget = "1.8"
}
}

dependencies {
coreLibraryDesugaring 'com.android.tools:desugar_jdk_libs:'
}

[boguszpawlowski]

Hi @jeongth9446! Sorry that it took me so long to answer this. I think adding a reference is a good idea, however, I would only add a link to an official documentation: https://developer.android.com/studio/write/java8-support. IMO, setup section would be the best place for it. If you want to submit a PR, feel free to do so.