added a basic working JS compiler maven plugin (though it doesn't currently let you specify any library files to compile)

libraries/examples/js-example/src/main/kotlin/sample/Hello.kt

@@ -1,7 +1,9 @@
 package sample
 
 class Hello {
+    var x = 0
+
     fun doSomething(): Unit {
-        println("Hello world!")
+        x++
     }
 }