Allow applying kapt and using mixins in other source sets (#211)

* Fix kapt and source sets

* cleanup

* cleanup 2

build.gradle

@@ -62,6 +62,9 @@ dependencies {
 	// source code remapping
 	implementation ('org.cadixdev:mercury:0.1.0.fabric-SNAPSHOT')
 
+	// Kapt integration
+	compileOnly("org.jetbrains.kotlin:kotlin-gradle-plugin:1.3.72")
+
 	// Testing
 	testImplementation(gradleTestKit())
 	testImplementation("org.spockframework:spock-core:1.3-groovy-2.4")