v4.0.0-eap

• migrate code to #Kotlin
• reduce code by 60% – 644KB to 262KB
• fix ALL compatibility issues with 2020.3
• introduce detekt for better code quality
• code cleanup (drop Git/Mercurial dead already features)
• plugin is now dynamic (install/uninstall without IDE restarting)
• introduce better CI – based on the IntelliJ Platform Plugin Template
• upgrade all Grammar-Kit, Gradle tooling
• focus on always supporting the latest release (only): currently 2020.3