Adding data classes with md file for tutorial purposes

src/halil/raso/com/tutorials/dataclasses/dataclass.kt

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+package halil.raso.com.tutorials.dataclasses
+
+fun main(args : Array<String>) { //entry point of any kotlin program.
+    val usr1 = User(name = "Halil", age = 32) // we create an object of a data class User
+    println(usr1.toString()) // This is equivalent to println(user1).
+    val usr2 = usr1.copy(name= "Khalil", age = 31)
+    println(usr2) // Will print: User(name=Halil, age=31)
+    val usr3 = usr1; // Equivalent to copy mehtod.
+    usr3.age= 33;
+    println(usr3) // Will print: User(name=Halil, age=33)
+    println(usr3.component1())// Getting the first parameter of object.
+}
+
+data class User(val name: String, var age: Int)

src/halil/raso/com/tutorials/dataclasses/dataclasses.md

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+Most of classes we defined or used are for storing data purposes.
+For those classes are define in general:
+1- A constructor. 
+2- Fields to store data.
+3- getter and setter methods.
+4- hashCode(), equals and toString() methods.
+Data Class of Kotlin comes in scene and rescue us from doing such boring tasks.
+It will useful to think Kotlin data class as Java beans.
+General syntax of defining such classes is as following: 
+data class Class_name(val/var param1, ...., val/var paramn).
+Important Note: If you are only interested in getter, you should define
+the corresponding parameter as val not var. 
+* If you are interested in getting the first parameters without regarding 
+its name, you could use component1() function. This is called destruction.
+
+