start studying memento pattern

Author: sensorario

README.md

@@ -10,6 +10,7 @@
  * [Strategy](behavioral/strategy) [:notebook:](https://en.wikipedia.org/wiki/Strategy_pattern)
  * [Command](behavioral/command) [:notebook:](https://en.wikipedia.org/wiki/Command_pattern)
  * [Template](behavioral/template) [:notebook:](https://en.wikipedia.org/wiki/Template_pattern)
+ * [Memento](behavioral/memento) [:notebook:](https://en.wikipedia.org/wiki/Memento_pattern)
 
 ## [Creational](creational)
 

behavioral/README.md

@@ -8,3 +8,4 @@ We are going to deal with behaviors instead of define structures or encapsulate
  * [Chain of Responsibility](chain) [:notebook:](https://en.wikipedia.org/wiki/Chain-of-responsibility_pattern)
  * [Command](command) [:notebook:](https://en.wikipedia.org/wiki/Command_pattern)
  * [Template](template) [:notebook:](https://en.wikipedia.org/wiki/Template_pattern)
+ * [Memento](memento) [:notebook:](https://en.wikipedia.org/wiki/Memento_pattern)

behavioral/memento/README.md

@@ -0,0 +1,20 @@
+# Behavioral » Memento
+
+## Description
+
+The memento pattern provides the ability to restore an object to its previous
+state (undo via rollback). It is implemented with three elements:
+
+ - originator
+ - caretaker
+ - memento
+
+The originator is an object that has an internal state. The caretaker change
+the originator's state, but wants to be able to undo the change. The caretaker
+first asks the originator for a memento object. Then it does whatever operation
+it was going to do. To roll back it returns the memento object to the
+originator.
+
+
+## Implementation
+