Pill: Introduce pill{} extension to set extended Pill configuration

Also introduce the flavor concept which allows to specify what part of Kotlin project should be imported.

custom-dependencies/protobuf-relocated/build.gradle.kts

@@ -3,6 +3,7 @@ import java.io.File
 
 plugins {
     base
+    id("pill-configurable")
 }
 
 val baseProtobuf by configurations.creating
@@ -18,7 +19,9 @@ val renamedSources = "$buildDir/renamedSrc/"
 val outputJarsPath = "$buildDir/libs"
 val artifactBaseName = "protobuf-java-relocated"
 
-val jpsLibraryPath by extra(outputJarsPath)
+pill {
+    libraryPath = File(outputJarsPath)
+}
 
 setProperty("archivesBaseName", "$artifactBaseName-$protobufVersion")