superclass in Kotlin

Code in a derived class can call its superclass functions and property accessors implementations using the super keyword:
```
open class Rectangle {
    open fun draw() { println("Drawing a rectangle") }
    val borderColor: String get() = "black"
}

class FilledRectangle : Rectangle() {
    override fun draw() {
        super.draw()
        println("Filling the rectangle")
    }
    val fillColor: String get() = super.borderColor
}
```
Inside an inner class, accessing the superclass of the outer class is done with the super keyword qualified with the outer class name: super@Outer:
```
class FilledRectangle: Rectangle() {
    override fun draw() { 
        val filler = Filler()
        filler.drawAndFill()
    }

    inner class Filler {
        fun fill() { println("Filling") }
        fun drawAndFill() {
            super@FilledRectangle.draw() // Calls Rectangle's implementation of draw()
            fill()
            println("Drawn a filled rectangle with color ${super@FilledRectangle.borderColor}") // Uses Rectangle's implementation of borderColor's get()
        }
    }
}
```
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