0.8.4 released

Major changes:

• Add com.android.feature to the set of supported plugins (#192)
• Make IntelliJ aware of *.proto and generated *.java files (#193), #198)
• Support for Kotlin (#196, #208) and Kotlin Android (#201)
• Support for Android local unit tests (#209)

Minor changes:

• Fix Gradle warning related to TaskInput.file API (#172)
• Avoid calling protoc with too many arguments (mainly affecting Windows) (#174)