Update gradle and dependencies, Migrate to MavenCentral

[akexorcist]

What's changes

• Update Gradle & dependencies
  • Gradle 7.5.1
  • Kotlin 1.7.20
  • JUnit 4.13.2
  • Gson 2.10
• Migrate AreaJavaTest.java to Kotlin
• Fix lint warning
• Use com.palantir.git-version for Git tag version retrieving
• Migrate Kotlin test assertion to JUnit assertion
• Migrate Bintray - JCenter to Sonatype - MavenCentral (See [Sunsetting of JCenter](https://jfrog.com/blog/into-the-sunset-bintray-jcenter-gocenter-and-chartcenter/))

Deploy the library to MavenCentral

• Complete the prerequisite instruction Publishing my artifact - Getting started
• Go to OSS Sonatype. Log in and go to your profile to access your user token (username and password for publishing)

Manual Deployment

• Create local.properties at root project
• Add your credentials in local.properties

• Don't worry, this file was ignored from Git (see .gitignore)

ossrhUsername=<username>
ossrhPassword=<password>

• Use ./gradlew clean build to build the library
• Use ./gradlew publish to publish the library to Sonatype
• Go to OSS Sonatype - Repository to accept your library package
• Wait for 1-10 minutes then refresh your library package to deploy it
• All done

Deploy with Travis CI

See Solid CI with GitHub, TravisCI and Sonatype Nexus

Use https://s01.oss.sonatype.org instead of https://oss.sonatype.org

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Feel free to ask me if you have a problem about library publishing