#1469 Add lambda expressions implementation for Strategy Pattern (#1631)

* #1469 Add Strategy Pattern lambda implementation

After Java 8.
Also take advantage of enum

* #1469 Update class diagrams

* #1469 Update README.md

Add lambda programmatic example

* #1469 Remove unused imports

Co-authored-by: Subhrodip Mohanta <subhrodipmohanta@gmail.com>

strategy/etc/strategy.urm.puml

@@ -14,6 +14,19 @@ package com.iluwatar.strategy {
   interface DragonSlayingStrategy {
     + execute() {abstract}
   }
+  class LambdaStrategy {
+    - LOGGER : Logger {static}
+    + LambdaStrategy()
+  }
+  enum Strategy {
+    + MeleeStrategy {static}
+    + ProjectileStrategy {static}
+    + SpellStrategy {static}
+    - dragonSlayingStrategy : DragonSlayingStrategy
+    + execute()
+    + valueOf(name : String) : Strategy {static}
+    + values() : Strategy[] {static}
+  }
   class MeleeStrategy {
     - LOGGER : Logger {static}
     + MeleeStrategy()
@@ -30,7 +43,10 @@ package com.iluwatar.strategy {
     + execute()
   }
 }
+Strategy ..+ LambdaStrategy
+Strategy -->  "-dragonSlayingStrategy" DragonSlayingStrategy
 DragonSlayer -->  "-strategy" DragonSlayingStrategy
+Strategy ..|> DragonSlayingStrategy 
 MeleeStrategy ..|> DragonSlayingStrategy 
 ProjectileStrategy ..|> DragonSlayingStrategy 
 SpellStrategy ..|> DragonSlayingStrategy