Added State pattern

Author: neoneye

README.markdown

@@ -345,6 +345,51 @@ tuple.z
 ##Memento
 ##Observer
 ##State
+
+```swift
+class Context {
+	private var state: State = UnauthorizedState()
+	func changeStateToAuthorized(#userId: String) {
+		state = AuthorizedState(userId: userId)
+	}
+	func changeStateToUnauthorized() {
+		state = UnauthorizedState()
+	}
+	var isAuthorized: Bool {
+		get { return state.isAuthorized(self) }
+	}
+	var userId: String? {
+		get { return state.userId(self) }
+	}
+}
+
+protocol State {
+	func isAuthorized(context: Context) -> Bool
+	func userId(context: Context) -> String?
+}
+
+class UnauthorizedState: State {
+	func isAuthorized(context: Context) -> Bool { return false }
+	func userId(context: Context) -> String? { return nil }
+}
+
+class AuthorizedState: State {
+	let userId: String
+	init(userId: String) { self.userId = userId }
+	func isAuthorized(context: Context) -> Bool { return true }
+	func userId(context: Context) -> String? { return userId }
+}
+```
+**Usage:**
+```swift
+let c = Context()
+println("\(c.isAuthorized), \(c.userId)")
+c.changeStateToAuthorized(userId: "admin")
+println("\(c.isAuthorized), \(c.userId)")
+c.changeStateToUnauthorized()
+println("\(c.isAuthorized), \(c.userId)")
+```
+
 ##Strategy
 
 ```swift