Add List<T>.shifted function

Author: Zomis

games-core/src/main/kotlin/net/zomis/games/common/GameLists.kt

@@ -1,3 +1,8 @@
 package net.zomis.games.common
 
 fun <T: Any> T.toSingleList(): List<T> = listOf(this)
+fun <T> List<T>.shifted(steps: Int): List<T> {
+    require(steps >= 0)
+    require(steps < this.size)
+    return this.subList(steps, this.size) + this.subList(0, steps)
+}