Add Gradle support

[Derpthemeus]

Adds Gradle build support. My motivation for doing so was so that I could use https://jitpack.io/ to easily add rars as a dependency to another project I'm working on.

Files autogenerated by IntelliJ. build.gradle configured to have the same behavior as build-jar.sh (includes both .class and .java files in the .jar file)

[TheThirdOne]

I have not yet setup gradle because I do not particularly care to have the standard wrapper in the repo. I favor simple solutions and the current bash script is definitely more simple. I am unsure if gradle as introduced in this PR is worth it to include.

If your only reason for RARS to use gradle is jitpack, can't you set up the dependency to a tag. I am not familiar with it, but implementation 'com.github.TheThirdOne:RARS:v1.6' should work.

[Derpthemeus]

Jitpack fails to build the repo with the error No build file found. Looking for Gradle/Maven/Sbt/Lein build file in the root of the project. https://jitpack.io/com/github/TheThirdOne/rars/v1.6/build.log

Let me know if you have any issues with Gradle specifically. I could add Maven/Sbt/Lein buildfiles instead if you prefer one of those systems